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WORLD-LIFE 



OR 



COMPARATIVE GEOLOGY 



BY 



ALEXANDER WINCHELL, LL.D., 

Professor or Geology and Paleontology in the University or 
Michigan. 



Geology in framing its conclusions is compelled to take into account the 
teachings of other sciences.— Sir William Thomson. 

La geologie suivie sous ce point de vue qui la rattache a T Astronomic pour- 
ra, sur beaucoup d'objets, en acquerir la precision et la certitude.— Laplace. 

Ewig zerstort, es erzeugt sich ewig die drehende Schopfung, 

Und ein stilles Gesetz lenkt der Verwandlungen Spiel. — Schiller. 




CHICAGO 

S. C. GRIGGS AND COMPANY. 

18 83. 



COPTKIGHT. 1883, 

By S. C. GRIGGS AXD COMPANY. 



.'i^ 






^ TO 



HIS PUPILS IN THE UNIVERSITY OF MICHIGAN, 

THIS VOLUME IS, 

WITH PROFOUND CONSIDERATION, 

AFFECTIONATELY INSCRIBED 
BY 

THE AUTHOR. 



PREFACE. 



r mHE reader will find in the following pages a thoughtful view of 
-*- the processes of world formation, world growth and world deca- 
dence. I have gathered together here many of the important facts 
observed in the constitution and course of nature, and have endeav- 
ored to weave them into a system by the connecting threads of scien- 
tific inference. I have aimed to incorporate the soundest and latest 
views published on the various branches of the subject; and have 
yet felt constrained, in so wide a field, and so unexplored in some of 
its nooks, to interpose my own conclusions in some cases where, 
perhaps, due diffidence should have restrained my pen. Inevitably 
the whole discussion is conducted from the standpoint of nebular 
cosmogony. This, as will be seen, has shaped the views presented 
on the accumulation of the materials for world formation, on the 
evolutions of nebulae, stars and planets, on the all-important influ- 
ence of tidal action in cosmic history, and on the grand cycle of 
cosmic existence. Appropriately the treatment ends with a histori- 
cal sketch of the progress of opinion toward the lofty and inspiring 
generalization which the work attempts to set forth. 

The motives which have prompted to the preparation of the 
work are four-fold . 

1. I felt desirous that the general reader should be able to find 
within reach some simple, yet complete and connected, account of 
the development of the world and the system of material things to 
which we belong. Many of the grandest conceptions of modern 
science fall within this range. Many of the marked advances of 
modern investigation have contributed to the enlargement of our 
view in this field. Yet there is no work in the English language, if, 
indeed, in any language, bringing into one connected course of dis- 
cussion all the questions properly incident to the activities of world. 



Yl PREFACE. 

life. Different persons have ably investigated different branches 
of the general theme, as the reader will learn in the sequel, but 
no one has brought together and put in the form of popular state- 
ment the chief results of so diversified a range of researches. 
Many thousands of intelligent listeners have testified their appreci- . 
at ion of the expositions offered during fifteen years past from the 
popular platform; but these expositions have been necessarily de- 
scriptive and superficial, while many questions and many difficulties 
raised by the hearer had to be left unanswered. Here the speaker 
sits down to a sober talk with those who wish to listen further. I 
hope, therefore, the present work will find a welcome among the 
multitudes who have caught mere glimpses of the great doctrine, as 
well as the large class of readers in general who require something 
more substantial than our popular, fictitious tales of society. 

2. I desired to offer the reader a portrayal of the grand system 
of the universe, and leave him with a profound impression of the 
omnipresence and supremacy of One Intelligence. The unity and 
interdependence of all parts of ihs cosmic mechanism, from nebula 
to river delta ; the universality of nature's forces, and the uniform- 
ity of nature's modes of activity, all the way down from the galaxy 
to the little cascade in the glen, are facts of such stupendous and 
impressive significance as to stir the imagination and arouse the 
most torpid soul. This w6nderful concatenation of things when 
once glimpsed by the timid doubter, must force a conviction of the 
continuity of material existence ; and whoever has gained that con- 
viction, and will faithfully question his own consciousness, will soon 
be convinced that that which is interpreted, and can only be inter- 
preted, in terms of mechanism, cannot be self- originated, however 
remote its origin ; nor self-acting, however vast its extent or incom- 
prehensible its activities. 

3. I desired to induct the earnest student of nature, young or 
old, into the vestibule of celestial mechanics, and leave him with 
an inspiration which should carry him on to the pursuit of the 
higher methods of physical investigation. I have hoped, also, to 
show him that the fields of truth are not fenced off from each other 
and limited by the narrow definitions of the sciences. The fences 
are all down, and it is all one domain. The geologist tries to work 



PREFACE. VU 

out the constitution and life history of our planet. For the study 
of its accessible parts he needs to use the appliances and results 
of the whole round of the sciences. To its interior he cannot pene- 
trate; but he finds the planet journeying on a course of change 
which leads directly from a state of high primitive incandescence ; 
and, lifting his eyes, he beholds the incandescent state as a common 
incident in the vicissitudes of worlds. He cannot transport himself 
across the intervals of geologic aeons, but he can gaze upon other 
worlds just entering upon states passed millions of years ago by our 
earth; or states, even, which will be reached by our planet some 
millions of years in the future. I have attempted to take the reader 
over the system of evidences from which he may thus reason in 
laying the foundations of a science which, from one point of view, 
may be styled the geology of the stars; and, from another, the 
astronomy of the earth. It is the science of Comparative Geology. 
It is Astrogeology. It yields to no science in the fruitfulness and 
fascination of its conceptions. 

4. It has been a part of my purpose, also, to clear up the most 
serious difficulties encountered by belief in the nebular origin of 
our planetary system. At the present day the objections heard do 
not proceed to any considerable extent from proper representatives 
of scientific opinion, but from intelligent persons who fear that the 
interests of religious faith are jeopardized by the acceptance of any 
form of evolution. Some of these have honored me by very special 
attentions. They have challenged me to controversy, and their 
abettors have sometimes jeered me over my assumed inability to rise 
from the pile of ruins which has been made of me and my theory. 
I need not disguise the satisfaction which I feel in the arrival of the 
convenient time when these gentle gladiators shall discover them- 
selves battering their blades against a wall. 

While the fundamental conception underlying the course of 
reasoning here pursued is that of nebular evolution ; and while the 
general method of the evolution conforms to the celebrated hypothe- 
sis of Laplace, it would be an error to conceive the present work an 
attempt to establish the "hypothesis of Laplace." In the first 
place, the general principles of nebular cosmogony were the growth 
of a century and a half ; and the ideas contributed by Kant and Sir 



Vlll PREFACE. 

William Hersehel were certainly not less guiding and determinative 
than the services of the Marquis de Laplace. In the next place, the 
development of the doctrine has continued ever since the Sysfhue 
di( Monde was published. Since the invention of the spectroscope, 
the nebular cosmogony has undergone important modifications. A 
number of the ablest investigators of the present generation have 
given their best efforts toward putting the general doctrine in a 
consistent shape. Nor can it be correctly said that the general the- 
ory remains still in the status of a hypothesis. In certain points of 
detail, opinion may still remain divided ; but when a hypothesis has 
stood the scrutiny of three generations, and has become all but 
unanimously accepted by those prepared to form original opinions, 
as the real expression of a method in nature, surely, then, the time 
has passed when any person can advantageously illustrate his learn- 
ing and sagacity by continuing to reproach the conception as "a 
mere hypothesis." If any " mere hypothesis" ever strengthened into 
the condition of a scientific doctrine, assuredly we find in the scien- 
tific world to-day the general features ot a sound nebular doctrine. 

In style and treatment the present work possesses a double char- 
acter. The general reader may confine himself to the body of the 
discussion, unterrified by the nature of the foot notes, and find a 
simple, continuous treatment of the theme which. I hope, will sat- 
isfy his expectations. But if any one desires to know by what 
means some of the statements of the text have been established, he 
will find frequently in the foot notes the indications of simple 
mathematical operations, which may yield him some additional 
gratification. And if he feel prompted to pursue still further any 
branch of the inquiry, the accompanying references to the literature 
of the subject will enable him to follow the masters of science into 
their most recondite investigations. Thus, for one class, the book is 
suited to be read rapidly and laid aside : for another class it is a 
text book which may be studied. 

The general conception of world life here set forth has occupied 
the author's thoughts for many years ; and by writing and by popu- 
lar lectures, as well as before university classes, he has endeavored 
to disseminate truthful and inspiring estimates of the method of 
the world's growth. He has stood for the defence of nebular theory 



PKEFACE. IX 

when it had few friends, and when its enemies were prompted as 
much by sentiment as by good reason. The great idea was fascinat- 
ing; its magnificence took possession of the imagination, and its 
symmetry and coherence commanded rational conviction. It now 
commands the admiration and championship of the scientific world. 
I feel that it is entirely improbable that all errors of statement 
have been avoided through all the details of the discussion. The 
intelligent reader will discover many points where I have had to cut 
loose from the moorings of high authority and venture among the 
breakers of independent speculation. It is only Justice to myself, 
also, to state that all the main positions of the work were taken 
and reduced to writing more than two years ago. Many of those 
which at the time were new, or seemed to be new, were presented in 
public lectures as early as 1878 and 1879. Since these dates many 
advances in observation and in theory have been made, and not a 
few along those very lines which I had worked out. Since my first 
enunciations, Nordenskjold, Tissandier and the British Association 
have done much to establish the doctrine of disseminated cosmical 
dust; Sir. W. Siemens has published his speculations on the sources 
of the sun's heat; M. Faye has investigated the geology of the 
moon; Mr. (now Professor) G. H. Darwin has published his beauti- 
ful analytical investigations of the evolution of a rotating viscous 
spheroid; and Rev. 0. Fisher has collected in a handsome volume 
his researches on the physics of the earth's crust. If there remain 
any thoughts or suggestions which may fairly be ascribed to the 
author of this work, the scientific reader will find it out ; and I have 
only to hope that they may be found adequately supported by evi- 
dence; and, finally, that the whole discussion may afford the reader 
a degree of pleasure equal to that experienced by the writer in 
bringing the discussion to its present shape. 

University of Michigan, September, 1883. 



COISTTET^TS. 



PART I. 

WORLD STUFF. 
CHAPTER I. 

COSMICAL DUST. 

§ 1. Meteors. 

1. Phenomena and Physical Characters _ . , , 3 

2. Meteoroidal Orbits 17 

§ 2. Zodiacal Light 23 

§ 3. Comets 27 

1. Phenomena and Constitution . _ . _ _ 27 

2. Connection of Comets and Meteors . _ . _ 33 
§ 4. Saturnian Rings .._.._. .35 
§ 5. Nebula 35 

1. Their Existence 35 

2. The Spectroscope and Its Applications _ _ > 37 

3. Forms of Nebula? 42 

§ 6. Universal World Stuff _...__ 48 

1. Theory of Cosmical Dust ... . . _ .48 

2. • Theory of Elemental Atoms 49 

(L) History of Opinions 49 

(2.) Siemens' Hypothesis Concerning Solar Heat . 56 

§ 7. A Cosmical Speculation 65 

1. Aggregation of Cosmical Matter _ . _ . 65 

2. Cosmical Matter as a Resisting Medium . . .70 

3. Genesis of Nebulas and Comets .... 71 

4. Vicissitudes of Comets within Our System . . .74 

xi 



Xll COlsTTENTS. 



CHAPTER II. 

:nebular life. 
§ 1. Nebular Heat ...__. ..81 

1. Heat Produced by Refrigerative Contraction _ _ 81 

2. Changes in the Forms of Nebulge . _ .- . .87 

3. Heat Arising from the Aggregative Process . . 92 
§ 2. Nebular Rotation 94 

1. Causes of Rotation . . . . . . . 94 

2. Causes of Nebular Forms _.■_.. 99 

3. Influence of Resisting Medium .... 104 

4. Nebular Evolution without Rotation . _ _ , 105 
§ 3, Nebular Anxulation _ _ _ . . * . 106 

1. The Law of Equal Areas lOG 

2. Abandonment of a Ring 110 

3. Determination of the Width of the Ring ... Ill 

4. Non-Annulating Nebula? and Stratified Rings . . 118 
§ 4. Spheratiox of Rings 119 

1. Disruption of a Ring 119 

2. Rotation of Resulting Mass . . . . .121 

3. Influence of Cosmic Tides 129 

4. Ultimate Sjmchronism of Axial and Orbital Motions . 134 

5. Summary of Laws of Rotation . . . .134 

6. Arrangement of Heavier Matters on the Derived Sphe- 

roid 137 

7. Orders of Nebulae 139 



CONTENTS. Xlll 

PART II. 

PLANETOLOGY. 
CHAPTER I. 

ORIGIN OF THE SOLAR SYSTEM. 

§ 1. Verification of Nebular. Theory from Facts . . 147 

1. Phenomena of the Solar System . _ _ . 147 

A. Demonstrative Phenomena 147 

B. Phenomena Apparently Confirmatory . . 149 

2. Phenomena External to the Solar System . _ _ 150 
§ 2. Objections Based on Relations of Planetary Motions 153 

1. Retrograde Motions .._____ 153 

(1.) Caused by Perturbative Attractions . _ 154 

(2.) Caused by Coalescence of Planetary Constituents . 157 
(3.) Caused by a Certain Relation of Rotary Motion of 

the Nebula 157 

(4.) M. Faye's Explanation _ . _ _ _ 158 

2. The Periodic Times Too Long . . . _ .158 

(1.) Effect of Subsequent Planetanon _ . .159 
(2.) Effect of Great Central Condensation of the Annu- 

lating Spheroid 161 

3. The Periodic Times Too Short 167 

4. The Periodic Time of Phobos Too Short . . .168 

5. No Adequate Cause for Rotary Motion ... 170 
§ 3. Objections Based on Relations of Planetary Positions 171 

1. Orbital Inclinations _ . ... . . 171 

2. Interplanetary Intervals . . . . - - 173 

3. Elliptic Forms of Orbits 173 

(1.) Effect of Subsequent Planetation . . .174 
(2.) Effect of Perturbative Influences ... 175 
§ 4. Objections Based on Relations of Planetary Masses 
AND Densities 175 



XIV COKTEKTS. 

1. The Aggregate Asteroidal Mass Too Small _ . 175 

2. Disrupted State of the Asteroidal Mass . _ _ 176 

(1.) Contingencies of a Stratified Ring ... 176 
(3.) Possible Fate of an Intra-Jovian Ring . _ 177 

(3.) Effect of Excessive Undulations in a Fluid Ring 177 

3. Low Densities of the Exterior Planets .... 177 
§ 5. Objection Based on Relation to Terrestrial Duration 179 
§ 6. Objections Based on Relations of Comets, Stars and 

Nebula 181 

1. The Comets Irreconcilable with the Theory . . 181 

(1.) Neither Laplace nor Other Astronomers have In- 
cluded Comets in Our System's Nebular History . 182 

(2.) Some Comets must Approximate Planetary Condi- 
tions 183 

(3.) The Physical Relations of Comets to Our System are 
Acquired _ . 183 

2. Matter of Requisite Tenuity could Not Exist . . 184 

3. The Separation of a Ring Improbable .... 186 

(1.) Reason and Observation Affirm the Possibility . 186 
(2.) M. Faye's Objections Considered . _ . .187 

4. The Diverse Constitution of the Fixed Stars . . 191 

(1.) No Universal Homogeneity of Matter Assumed . 191 
(2.) Stellar Spectra Testify the Opposite of the Claim 191 

5. Nebular Spectra Indicate Too Low a Pressure _ - 192 

(1.) Nebular Theory is Not Staked on Spectra of Neb- 

ulfe 192 

(2.) The Spectra do Testify a Self-luminous, Tenuous 

Vapor ^ . .192 

(3.) Adverse Spectral Evidence Outweighed . . 193 
§ 7. What the Nebular Theory does Not Imply _ . . 196 
§ 8. Proposed Modified Forms of Nebular Theory . _ 198 

1. M. Faye's Proposed Modification 198 

Critical Remarks on M. Faye's Theory . . . 208 

2. Spiller's Proposed Modification 213 



CONTENTS. XV 



CHAPTER II. 

GENERAL COSMOGONIC CONDITIONS ON A COOLING PLANET. 

§ 1. Relative Ages of Planets ix a System . _ . _ 315 

§ 2. Passage to the Molten Phase _ . . _ . 217 

§ 3. Superficial Solidification From Cooling . . . 218 

§ 4. Internal Solidification From Pressure _ . _ 220 

§ 5. Maximum Internal Temperature on an Incrusted Planet 221 

§ 6. Tidal Action and Its Consequences . _ . . 222 

1. Some Elementary Principles 222 

2. General Effects of Tidal Action in Planetary Life . 230 

(1.) Rotational Retardation Caused by Lagging Tide 232 
(2.) Recession of Tide-Producer Resulting from Same 239 
(3.) Increased Inclination of Axis of Tide-Bearer Re- 
sulting from Same 243 

3. Tendency to Synchronism of Rotary and Orbital Motions 248 

4. Predetermination of Submeridional Trends . _ . 252 

5. Outflow of Molten Matter 255 

6. Crushing Effects of Tidal Deformation . , .255 

7. Marine Tides in the Early History of a Planet . . 256 

§ 7. Liquefaction of Water 270 

§ 8. Transformations of the Planetary Crust . _ _ 274 
§ 9. Planetographic Effects of Certain Changed Astro- 
nomical Conditions ._.._.. 278 

1. Changes in Velocity of Rotation . . _ . 278 

2. Retarded Orbital Motion 281 

3'. Increase of Obliquity of Axis to Plane of Orbit . 282 

4. Change in Relative Positions of Apsides and Equinoxes . 285 

5. Changes of Orbital Eccentricity . . . _ 288 
§ 10. Orogenic Forces 291 

1. Theory of Upheaval by Aeriform Agents . . . 292 

2. Theory of a Molten Nucleus and a Wrinkling Crust . 294 

3. Theory of Copious Sedimentation along Geosynclinals 314 



XVI CONTENTS. 

4. Theory of Mashing Togetlier 319 

5. Statement of Separate Constructive Conceptions Rela- 

tive to Mountain Making .__... 323 

6. Final Conception of Orogenic History . . . 326 

7. Analytical Conspectus of Orogenic Speculations _ _ 331 
§ 11. Unequal Thickness of Planetary Crust . _ . 335 

CHAPTER III. 
SPECIAL planetology; or, present condition and 

COSMOGONIC HISTORY OF THE PLANETARY BODIES OF 
OUR SYSTEM. 

§ 1. The Earth 338 

1. Condition of the Earth's Interior .... 339 

(1.) Fluidity of a Certain Zone 344 

(2.) Fluidity Resulting from Relief of Pressure . 345 
(3.) Tidal Deformation and Volcanic Phenomena . 346 

2. Submeridional Trends in the Earth's Primitive Structure 350 

3. The Earth's Age, with Methods of Estimation . . 355 

(1.) Time Required for Contraction of the Sun . 355 
(2.) Time Required for Cooling of the Sun . . 356 

(3.) Time Required for Cooling of the Earth . . 356 
(4.) Time Required for Deposition of All the Rocky 

Sediments 356 

(5.) Method Based on Disturbance from Continental 

Elevation 366 

(6.) Calculation Based on Secular Variation of Eccen- 
tricity ... 368 

(7.) Estimates Based on Rates of Erosion and Deposition 369 
(8.) The Rate of Terrace Formation . . . .374 
(9.) Under-rate of Increase of Internal Heat beneath 
Regions Anciently Covered by an Ice Cap . . 376 

g 2. The Moon 379 

1. Planetological Retrospect 379 



CONTENTS. xvn 

2. .Tidal Forces on the Moon . . - . .383 

3. Physical Aspects of the Moon 385 

4. Tidal Evolution of the Moon 395 

5. The Atmospheric Factor in Lunar History . . . 410 
§ 3. Mars 415 

1. Phenomena of Mars, and Their Interpretation . .. 415 

2. Tidal and Atmospheric Influences on Mars . . . 417 
§ 4. The Inferior Planets 420 

1. Venus 420 

2. Mercury .423 

§ 5. Jupiter , . _ 425 

1. Physical Relations _...... 425 

2. Jupiter's Retarded Development .... 429 

3. Tidal Action on Jupiter 434 

4. Tidal Effects and Densities on Jupiter's Satellites . 438 
§ 6. The Ultra-Jovian Planets 442 

CHAPTER IV. 

PLANETARY DECAY; OR, COSMIC CONDITIONS MORE 
ADVANCED THAN THE TERRESTRIAL STAGE. 

§ 1. Extremely Eroded Conditions . - . . . 451 

§ 2. Progressive Subsidence of Temperature . . . 458 

1. Shrinkage and Acceleration of Axial Motion . . 459 

2. Absorption of Water and Atmosphere . _ _ 460 

(1.) Index of Rock Absorption by Volume . . _ 460 
(2.) The Volume of the Ocean . . _ . 466 
(3.) Calculation of Absorptive Capacity of the Planet- 
ary Pores ...--._. 467 
§ 3. Synchronistic Motions and Tidal Finalitos . . 473 
§ 4. Influence of Interplanetary Matter .... 477 
§ 5. General Refrigeration 484 

1. Planetary Refrigeration 484 

2. Solar Refrigeration 484 



XVlll CO^iTTENTS. 

(1.) Inductive Evidences of Lowered Terrestrial Tem- 
perature - . _ 485 

(a) In Historic Times 485 

(6) In Prehistoric Times . . . - .485 
(c) Cause of Secular Deterioration of Climates . 486 

(2.) Deductive Considerations Touching Secular Cooling 489 
3. Revivification of a Dead Universe - . . . 491 

CHAPTER V. 

HA.BITABILITY OF OTHER WORLDS. 

§ 1. Some Referexces to Literature ox the Subject . . 496 
§ 3. The Humax Staxdard of Habitability Not Absolute . 497 
§ 3. Habitability uxder the Humax Staxdard . . _ 500 

PART III. 

GENERAL COSMOGONY. 
CHAPTER I. 

FIXED STARS AND XEBUL^. 
§ 1. COXDITIOXS OF THE FiXED StARS 511 

1. Double, Triple and Multiple Stars . . , . oil 

2. Temporary Stars 513 

3. Variable Stars 518 

4. Gradations of Stars 522 

5. Indications of Incipient Stellation .... 530 
§ 2. CosMOGOxic Conditions of Nebula _ .- . .531 

CHAPTER II. 

THE COSMIC CYCLE. 

§ 1. The Keys of Comparative Geology .... 534 

§ 2. The Final Generalization 538 

1. Stages of World Life ....-.- 538 

2. Some Final Deductions ..--.. 544 



CONTEi^"TS. XIX 

PART IV. 

EVOLUTION OF COSMOGONIC DOCTRINE. 
CHAPTER I. 

PRE-KANTIAN SPECULATIONS. 

§ 1. Greek Philosophers , . 551 

§ 2. Speculations of Kepler 553 

§ 3. The Vortical Theory of Descartes . . . _ 554 

§ 4. The Theory of Leibnitz 558 

1. His Protogaea . , . _ . . . . 558 

3. His Planetogeny 564 

§ 5. The Vortical Theory of Swedenborg .... 566 
§ 6. The Speculations of Thomas Wright . . . 573 

CHAPTER n. 

rant's general history of nature. 

§ 1. Firmamental Organization , 574 

§ 3. Planetogeny _ _ 577 

§ 3. The Cosmos in Its Totality 583 

§ 4. Our Sun and Other Suns 587 

§ 5. The Mechanical Constitution of the World . . 589 

§ 6. Deductions Touching Habitability and Unity in the 591 

System of Worlds 593 

§ 7. Synopsis of Points in the Cosmogonic Theory of Kant 

1. Points Considered Well Taken 593 

3. Points Considered Incorrectly Taken _ . - 595 

CHAPTER III. 

DR. LAMBERT AND SIR WILLIAM HERSCHEL. 

t* 1. Lambert's Cosmological Letters 597 



XX . CO]S^TElirTS. 

§ 2. Sir William Herschel's Researches . . _ . 598 

1. The Structure of the Heavens 528 

2. Nebular Studies . . _ . . > .601 

CHAPTER IV. 



§ 1. Prelimixary Views ox Xebulje axd General Physical 
Astronomy 606 

§ 2. Hypothesis Touching the Genesis of the Solar System 611 

1. Former Expansion of the Solar Atmosphere . . . 612 

2. Formation and Abandonment of Zones of Vapor . 613 

3. Rupture and Planetation of Rings _ . _ .614 

4. Relations of Comets and Zodiacal Liglit . , . 615 

5. Lunar Synchronistic ^Motions . . - _ . 615 

CHAPTER V. 

SYSTEMATIC RESUME OF OPIXIOXS. 



LIST OF ILLUSTRATIONS. 



1. Corpuscles of Magnetic Iron from the Snow on Mont Blanc 

at the Altitude of 2,710 Metres X500 . . - .10 
From Tissandier. 

2. Corpuscles of Magnetic Iron Collected from Rain Water at 

Sainte Marie du Mont X500 _ _ ... 10 

From Tissandier. 

3. Corpuscles of Magnetic Iron from the Dust Collected in the 

Unfrequented Towers of Notre Dame de Paris . . 10 

From Tissandier. 

4. Fall of a Bolide at Queengouck, India _ . _ _ 12 

From a Drawing by Lieutenant Aylesbury. 

5. The Positions of the August and November Meteoroidal 

Swarms _ _--19 

Compiled by the Author. 

6. The Great Nebula in Orion. Central Part . . „ 42 

From a Drawing by Trouvelot. 

7. Siekl^-shaped Nebula. Herschel 3,239 . . o . 43 

After Schellen. 

8. Spiral Nebula in Canes Venatici. Herschel 1,622 . .44 

After Schellen. 

9. Spiro-annular Nebula. Herschel 604 . _ _ _ 44 

After Schellen. 

10. Spiro-annular Nebula. Herschel 854. Indications of Sev- 
eral Rings . _ 45 

After Schellen. 

11. Annular Nebula in the Lyre 46 

From a Drawing by Professor Holden. 

12. Planetary Nebula, without a Nucleus. Herschel 2,241 . 46 

After Schellen. 

13. Planetary Nebula with two Nuclei. Herschel 838 . - 47 

After Schellen. 

14. Ideal Illustration of the Streams of Outflowing and Inflowing 
Matter on the Sun 60 

After Siemens. 

xxi 



XXU LIST OF ILLUSTRATIONS. 

15. Motion of a Body in the Presence of Two Other Bodies . 67 

Original. 

16. The Omega Nebula in Sagittarius . , . . . 89 

From a Drawing by Lasell in 1862. 

17. The Omega Nebula . . . . . . .90 

From a Drawing by Trouvelot and Holden in 1875. 

18. The Trifid Nebula " 91 

From a Drawing by Trouvelot. 

19. Motion of Three Nebulae in Space, Case I, Sub-case I .95 

Original. 

20. Motion of Three Nebulae in Space, Case I, Sub-case II _ 96 

Original. 

21. Motion of Three Nebulae in Space, Case II ... 97 

Original. 

22. Rotation Resulting without Actual Impact . . .98 

Original. 

23. Possible Origin of the Falcate Form of Nebula . . 103 

Original. 

24. Coagulating Nebula, or "Curdling Fire mist" _ . 105 

Original. 

25. Formation of Local Nuclei in a Nebula . . . 106 

Original. 

26. The " Law of Equal Areas " 108 

Original. 

27. Nebula in Process of Annulation 113 

Original. 

28. Illustrating the Determination of the Width of a Nebulous 
Ring - ... 114 

Original. 

29. Nebula Becoming Annular 117 

Original. 

30. Stratification of a Nebulous Ring 119 

Original. 

31. Nebulous Ring Undergoing Rupture . . _ . 120 

Original. 

32. Spheration of a Nebulous Ring 120 

Original. 

33. Prolateness and Rotation of the Derived Spheroid . . 130 

Original. 

34. Inversion of the Orbit of a Satellite . ^ o - 155 

Original. 



LIST OF ILLUSTRATIONS. XXlll 

35. Process of Lengthening the Periodic Time and Acquiring 

an Elliptic Orbit .160 

Original. 

36. Increase of Density toward the Centre of the Nebulous 
Spheroid . ..._--. 164 

Original. 

37. Deformative Tide 226 

Original. 

38. Compound Tide 226 

Original. 

39. Film Tide 227 

Original. 

40. Quantitative Relations of Tides . - _ . . 228 

Original. 

41. Illustrating a Lagging Tide 282 

Original. 

42. Illustrating the Secular Effects of Tides in a Rotating Vis- 
cous Spheroid 236 

Original. 

43. Discordant Tides of a Nucleus and Film . . „ 239 

Original. 

44. Varying Reaction Resulting from Varying Viscosity . 242 

Original. 

45. Tidal Increase and Diminution of Obliquity ... 245 

Original. 

46. The Tide-Bearer Viewed as Tide-Producer . . .246 

Original. 

47. Ascent of Isothermal Planes in a Planet's Crust . . 276 

Original. 

48. Climatic Effect of Increased Obliquity of a Planetary Axis 283 

Original. 

49. Climatic Effect of Change in Relative Positions of Apsides 
and Solstices . -_.--.. 287 

Original. 

50. Illustrating the Formation of Mountain Wrinkles . . 299 

After M. Alphonse Favre. 

51. Formation of Wrinkles in a Planetary Crust, with Parallel 
Contiguous Furrows . 300 

Original. 

52. Section through the Alps, Showing the Effects of Lateral 
Pressure 310 

After Heim. 



XXIV LIST OF ILLUSTRATIOis^S. 

53. Diagram of Niagara Gorge, Old and Xew . > . 370 

After Belt. 

54. Map of the Moon .__ 386 

After M. Faye. 

55. Section across the Crater Copernicus . _ . . 387 

After M. Faye. 

56. Map of the Crater Theophilus, and Surrounding Region - 388 

After Xeison. 

57. Action of an Internal Tide against the Crust . _ . 398 

Original. 

58. Effect of Discordant Lagging Tides .... 398 

Original. 

59. The Disappearance of the Land = _ - . . 455 

Original. 



PART I. 
WORLD-STUFF. 



Ante, mare et telliis, et, quod tegit omnia, coelum, 

Unus erat toto Naturae vultus in orbe, 

Q,uem dixere Chaos; rudis indigestaque moles; 

Nee quidquam, nisi pondns iners; congestaque eodem 

Non bene junctariim discordia semina rerum.— Ovid. 



WORLD-LIFE. 



CHAPTEE I. 
COSMICAL DUST. 

I know no recent observation in pliysical geograpliy more calculated to 
impret's deeply the imagination than the testimony of this presumably meteoric 
iron frona the most distant abysses of the ocean. To be told that mud gathers 
on the floor of these abysses at an extremely slow rate conveys but a vague 
notion of the tardiness of the process. But to learn that it gathers so slowly 
that the very star-dust which falls from outer space forms an appreciable part 
of it, brings home to us, as hardly anything else could do, the idea of undis- 
turbed and excessively slow accumulation.— Archibald Geikie. 

§ 1. METEORS. 

WHENCE comes the "Dust of Time?" There is 
nothing around which the dust of time does not 
gather. It accumulates among the shelters of the moun- 
tain cliffs. It falls upon ivy-mantled towers and ruined 
walls, and creates a rooting place for many a hardy herb, 
and a nidus for countless living germs. It clogs the 
water-passages from our roofs, and fills our cisterns with 
soils yielded by the atmosphere. It gathers about de- 
serted structures; it buries the foundations of columns 
and temples; and new temples are built upon founda- 
tions which have older foundations beneath them. The 
ancient cities of the East and of the West lie slumbering 
beneath the accumulations of this dust. Nineveh is rec- 
ognized only as a mound of earth. Troy lies almost be- 
neath the reach of Schliemann's spade. The cities of 

3 



4 COSMICAL DUST. 

Cyprus, the Morea, and the Roman Peninsula are but 
slowly undergoing fresh exposure to the light of day. 

Whence the dust which has buried walls and towers 
and cities ? Let us answer the question with soberness. 
The crumbling of wooden beams, and even of the solid 
stones, has supplied the larger portion of the debris which 
mantle the foundations of the ancient cities. Much of the 
soil w^hich gathers upon roofs and in the crevices of old 
walls has been lifted by the winds from bare field and 
dusty street. Even the snowy summits of the Alps * be- 
come stained by terrestrial particles borne by upward cur- 
rents into the mountain air. And yet I will venture the 
opinion that some dust comes to the earth daily ichich 
had never belonged to the earth before. Out from the 
depths of space — beyond the clouds — beyond the atmos- 
phere — from a granary of material germs which stock the 
empire of the blue sky, comes a perpetual but invisible 
rain of material atoms — like the evening dew, emerging 
from the transparency of space into a state of growing 
visibility.f 

This is a somewhat unfamiliar thought. I will endeavor 
to indicate the steps of evidence by which it is reached. 

First, the Meteors yield both suggestion and proof. 
That mysterious visitant which paints its luminous streak 
along the evening sky — sudden, brilliant, but evanescent 
— what is it ? And what does it signify? Mankind for 
ages have gazed upon it with contemplative awe. Ac- 
cording to most recent scientific opinion, it is a mass 
of matter from outer space, which has become entangled 
in the exterior limits of our atmosphere, and, impeded 
in its movements by atmospheric resistance, has been 

* M. Tissandier reports magnetic particles of iron dust at a lieight of 9,000 
feet on the slopes of Mont Blanc, and other elevated positions. 

+ It has been quite a surprise to the author to find a similar conception 
thrown out by an anonj'mous writer several years since {North American Re- 
vietv, xcix, 28, note, July, 1864.) 



METEORS. 5 

overcome by the attraction of the earth, and deflected 
into a new path. It now moves obliquely toward the 
earth. The condensation of the air in front, caused by 
its rapid movement, develops an intense heat. The cold 
meteor is lighted up; it glows for an instant, but the heat 
becomes so intense that its entire mass sometimes is con- 
verted into vapor and strewn along the sky, to shine as 
a luminous streak after the bolide has ceased to pursue its 
course. The train of incandescent vapor retains its lumi- 
nosity, at times, for one, two or five minutes, floating like 
a cobweb in the atmosphere,* and as it cools it fades from 

* During the meteoric sliower of November 14, 1868, Profess^or Mai-ia Mitch- 
ell noted a train which las-ted forty-four minutes, and underwent remarkable 
distortions of form. (See AmeTicaa Journal of Science^ II, xlvii, 400.) The 
same was seen by Professor J. R. Eastman at Washington, to last thirty min- 
utes {Report, November 23, 1868). The phenomenon has been discussed by 
Professor H. A. Newton {American Journal of Science, II, xlvii, 40S). Changes 
of form and position of meteoric trains have been mentioned by Sir John Her- 
schel and others. Professor E. E. Barnard, for instance, of Nashville, Tennes- 
see, writes to Nature (xxv, 173, December 22, 1881) that a meteoric train re- 
mained visible, November 16, to the naked eye, six minutes, and with telescopic 
aid, fifteen minutes, and floated meantime, four degrees. On the contrary. Ad- 
miral Krusenstern states that he saw, during his voyage around the world, the 
train of a fire-ball shine for an hour after the luminous body itself had disap- 
peared, and scarcely move throughout the whole time (Krusenstern : Etise, Th. i, 
S. 58). 

If the visibility of the train results from incandescence, it is difficult to un- 
derstand how it remains so long in an assemblage of particles fine and buoyant 
enough to float in the upper atmosphere. Is it an electric or a phosphorescent 
glow? Humboldt in a note {Cosmos, Ott.' trans. Harper ed., i, 142) says "sev- 
eral physical facts appear to indicate that in a mechanical separation of matter 
into its smallest particles, if the mass be very small in relation to the surface, 
the electrical tension may increase sufficiently for the production of light and 
heat." Thus, while we are forced to admit the first flash of a meteoric streak 
as implying actual incandescence, it seems not improbable that the fainter and 
prolonged glow is electric. In this connection I am reminded to cite a pas- 
sage from Professor Joseph Lovering: ''Finally, I may notice the light enjoyed 
in cloudy nights which cannot, Arago supposes, come from the stars, but from 
the phosphoi-escent clouds. It is never so dark out of doors as in a subterranean 
apartment, or in a room without windows. During the dry mist of 1783, the 
sky was as bright as during the full moon when overclouded. Is this light the 
glow-discharge of electricity? If so, has the solar light the same electrical origin 
more intensely developed? And is the colored light which Nicholson saw in 
the clouds on the 30th of July, 1797, the result of processes similar to those 
that give a color to certain of the stars which difl^er from the white sun-light? " 
(Lovering, Patent Office Report, 1855, Agriculture, 356.) 



6 COSMIC A L DUST. 

view. But let us not lose siofht of the matter which un- 
derwent ignition; it is not annihilated: it has not been 
returned to the regions beyond our atmosphere; those are 
physical impossibilities. Unseen, unheard, millions of 
particles of cooled vapor remain floating in our air. Be- 
ing ponderable, being mineral and mostly metallic, they 
must settle toward the earth. They are plunged into the 
vortices of the winds: they are soaked up by aqueous 
vapors; they are floated by clouds, they are washed down 
by rivers and added to the volume of the globe.* 

That this conclusion is well founded we have abundant 
evidence. Every one understands that the atmosphere is 
freighted with minute solid particles. These were elabo- 
ratelv investio^ated bv Ehrenbero; thirtv or forty years ag-o, 
who, like Pasteur and Tyndall in more recent researches, 
directed attention more especially to organic substances, 
particularly minute germs and bacterial organisms. Few 
people understand that the atmosphere bears also a large 
proportion of mineral substances, some of which must, 
almost to a certainty, have an extra-terrestrial origin, A 
careful compilation of facts has been made by M. Gaston 
Tissandier in his work on atmospheric dust.f 

As to atmospheric dust of terrestrial origin, investiga- 
tion shows that the larger part is taken up by winds from 
the deserts of Sahara and Gobi. The African dust lias 
descended in scores of recorded showers in all parts of 
Europe, as well as in the Atlantic ocean along a belt of 
1,500 miles, and as far as 300 miles from land. The Mon- 
golian dust falls chiefly in northern China, and is con- 
ceived bv Baron von Richthofen to be the source of a vast 



* The foregoing ob\ion? inferences were penned and made part of a lecture 
in 1877. Since that date the writer has discovered a large amount of evidence 
bearing on the question of cosmical dust, as the stiitements and references in 
the next following paragraphs will show. 

t Tissandier: Les pou^xleres de fair, Paris, 1877. See also Popular Science 
Monthly, xvii, W4-50, July, 1890. 



METEORS. 7 

geological deposit known as loess. The volcanoes of Java, 
Central America and Iceland have also emitted astonish- 
ing- volumes of dust which was floated hundreds of miles. 
Amongst organic substances found in nearly all parts of 
the world sometimes occur enormous quantities of pollen 
cells from forests of coniferous vegetation.* The particles 
of smoke arising from western forest and prairie fires are 
often wafted from Michigan and Wisconsin to Montreal 
and New York. There is no doubt that the characteristic 
smokiness of the atmosphere during the mild period in 
November following the occurrence of the first killing 
frosts, and known in America as the Indian Summer, 
is simply the smoke arising from the autumnal burnings 
of the recently killed and well dried vegetation of thinly 
settled districts. It may hence be inferred that this feature 
of the Indian Summer will grow, less characteristic as set- 
tlement more completely clears and cultivates the surface. 
But atmospheric dust of terrestrial origin has no bear- 
ing on our search for world-stuff. Among the earliest to 
suggest a cosmic origin for certain forms of atmospheric 
dust were Ehrenberg and Arago. The latter in his Popu- 
lar Astronomy f sa3''s it may be presumed that showers of 
dust do not differ materially from ordinary meteoric show- 
ers. The dust, he says, appears to contain the same sub- 
stances as meteoric stones. Ehrenberg states that one 
element in the colored snows examined by him was iron, 
and he expresses tlie hope that scientific men would accu- 

*The writer recalls an occaision in 1853 when in Alabama, on the morning 
after a shower, a j^ellow and sulphnr-like deposit was left wherever the water 
had been accumulated. Investigation showed the substance to consist of pol- 
len grains; and as the cypress swamps and pine forests of the Gnlf region were 
then in flower, the explanation was obvious. Similar " sulphur showers " have 
been since reported as far north as the Ohio river, and also in the countries of 
southern Europe. A case is recently reported in Iowa by C. E. Bessey. A77ier. 
Naturalist, xvii, 658, June, 1883. 

t Arago: Astronomie Populaire, t. iv, 208. See also (Euvres completes de 
Francois Arago, t. xii, 293, 463, etc. 



8 COSMICAL DUST. 

mulate the substance in quantity, and compare it in this 
state with fragments of aerolites, and inspect microscopi- 
cally the smallest globules. Baron Reichenbach in 1864* 
insisted on the probability that meteorites exist in the 
form of granules and dust, that they descend to the earth 
and add something to its quantity of matter. He also was 
apparently the first to detect nickel and cobalt in atmos- 
pheric dust, and these furnish the critical demonstration 
of its meteoric origin. M. Daubree, in his celebrated 
memoir on meteorites,t speaking of the meteorite of Or- 
gueil, says it is ''very instructive in reference to the exist- 
ence of meteoric dust," and proceeds to explain how the 
disintegration of such a body would supply it. Among 
the first to produce evidence in support of the theory of 
the cosmic origin of certain portions of the atmospheric 
dust was Baron A. E. Nordenskj5ld4 He reported large 
patches of arctic ice covered with a gray diatomaceous 
powder mingled with grains of magnetic iron surrounded 
by iron-oxide, and containing also probably carbon. Simi- 
lar deposits were reported from snows from the neighbor- 
hood of Stockholm, from the interior of Finland and from 
Spitzbergen. He reports the detection of nickel and 
cobalt in dust from the middle of Greenland, and states 
that he is personally convinced that certain hail from near 
Stockholm was formed around particles of cosmic origin 
floating in the air and falling continualh^ to the earth. 
He also indicates the presence of a brown carbonaceous 
material like that aiforded by the meteoric iron from 
Ovifak, which is characterized by a very disagreeable 
odor and seems to be organic. Baron Nordenskjold has 

* Reichenbach, Poggendorfs Antialen, cxxiii, 368-74, 1864: Cosmos, 29 Dec. 
1864. 

t Daubree, Journal des Savans, 1870. 

i See a note by M. Daiibn'e in Comptes Bendus, Ixxvii, 464, 18 Aug. 1873, 
and Ixxviii, 236, 26 Jan. 1874. Also Poggendorfs Annalen, cl, 154, 1874, and 
Am. Jovr. Sci., Ill, ix, 14.5-6. 



METEORS. 9 

more recently reported further observations.* He states 
that the snow of the coast of the Taimur peninsula was cov- 
ered with yellow specks of carbonate of lime of an unusual 
form of crystallization, and these he believed to be of 
interplanetary origin. The carbonate of lime found by 
others, as well as all organic traces, has generally been 
referred to a terrestrial origin; but this, after all, may be 
an error. 

At the meteorological station of Yeneseisk, Marx col- 
lected a quantity of brick-red dust which was brought 
down from the atmosphere during a gale, accompanied by 
snow and rain, October 31, 1881. An examination of 
this by Professor Lenz shows it to consist of iron, nickel 
and cobalt ; and he entertains no doubt of its cosmical 
origin, pointing out the fact that it was observed on a day 
very near to the appearance of the November meteors.f 

M. Tissandier has made quite extensive researches on 
atmospheric dust, and has put beyond question the mete- 
oric origin of certain portions of it. Many grains and 
minute globules of iron are met with in these dust-falls, 
which appear to have been fused ; and it is shown that 
in certain cases, nickel and cobalt are present in the iron, 
precisely as in siderolites. But in other cases these sub- 
stances are wanting, and these are cases where other indi- 
cations point to a tcrrestial origin. These grains of mag- 
netic iron have been collected from a great variety of 
situations — from the summit of Mont Blanc, from rains 
recently fallen, from the towers of Notre Dame cathedral 
in Paris and many other cathedrals, from the borders of 
Lake Lehman, from the hospice of St. Bernard and from 
many localities in distant countries. Everywhere are 

*Nordenskjold: The Voyage of the Vega round Asia and Europe. Trans- 
lated by Alexander Leslie, 2 vols, London, 1881. 

+ Lenz in Izvestia of the Russian Geographical Societj% 1883, cited in Nature, 
xxvii, 42-2, March 1, 1883. 



10 COSMICAL DUST. 

found these iron globules bearing the unmistakable marks 
of fusion. The following figures are copied from j\I. Tis- 
sandier's work : 

# ^ % # i 

Fig. 1. Corpuscles of Magnetic Iron, From the Snow of Mont Blanc 
AT THE Height of 2,710 Metres. X 500. 




Fig. 2. Corpuscles of Magnetic Iron Collected from Rain Wateh at 
?ainte Marie bu Mont, x 500. 



^ 4 




Fig. 3. Corpisci.ei^ of .Magnetic Iron from the Dust Collected in the 
Unfrequented Towers of Notre Dame de Paris, x 500. 

Most of the writers who recognize the meteoric origin 
of these grains conceive them as minute meteorites, while 
to me they seem rather to be the cooled particles of the 
volatilized bolide. When of small size, the bolide is com- 
pletely consumed, when too large for a destructive heat to 
penetrate to its centre during the brief interval of the 
body's descent through the atmosphere, it is only the surface 
wliich undergoes fusion, and this is swept off by the vio- 
lent impact of the air, and broken into countless minute 
particles. Hence the exterior of a fragment of meteoric 
iron presents those peculiar rounded bosses and concavi- 
ties developed on the surface of melting ice. 



METEORS. 11 

Occasionally these bolides attain to terrific dimensions. 
The accompanying illustration, also from Tissandier, repre- 
sents the bolide which preceded the fall of meteorites at 
Queengouck, India, on the 27th of December, 1857. The 
train shows the particles of molten mineral brushed off by 
the impact of the air. The drawing was executed by 
Lieutenant Aylesbury, an eye-witness of the phenomenon, 
and was first reproduced by Haidinger in his Etude sur la 
chute Queengouck. 

If Mr. Jolin Aitken's theory is correct, that the presence 
of solid particles is the condition of vapor-condensation, 
then the highest clouds of our atmosphere reveal the 
presence of a fine dust, and this very probably is of a cos- 
mic character.* 

A committee of the British Association appointed to in- 
vestigate this subject, reported through Professor Schuster 
in 1882, t that rounded particles of iron containing nickel 
and cobalt have been found in many situations, and we are 
constrained to ascribe them to a cosmic origin.:}: 

Thus the evidence of the perpetual arrival of foreign 
matter from the interplanetary spaces seems conclusive. 

* See Nalure, xxiii, 195-7, December 80, 1880. 

t See abstract in Nature, xxvii, 488. 

X The reader will fiiul a snmmarj- of the principal cases in the work of Tis- 
sandier. The following are some notices of more recent date. Tacchini re- 
ported iron in atmospheric dnst, siqyposed to be from the Sahara {Acadende des 
Sciences, 28 June, 1880). Professor Sylvestri of the Catania Observatory, re- 
ported a dust-fall with much metallic iron in Sicily, March 29-30, 1883 {Atti dei 
Ji. Acadtmia dei Lincei, fasc. 6, May, 1880: Nature, xxi, 574, xxii, 257). On 
Sicilian dust-falls, which have been particularly frequent, see Lancetta in his 
Synthesis of meteorological observations in Modica and Syracuse, on the fall of 
meteoric powders from the end of 187(5 to April 16, 1880 {Rerista Sclenlijica- 
ludustiiale. No. 15, August 1880). M. Daubree reports further dust-falls at 
Autun, April 15, 1880, and in the Departments of the Basses-Alpes, Isere and 
Ain, France, April 21-25, 1880 {Comptes Eeiidm, 10 Maj% 1880), as also in Algiers, 
April 24-2f;, 188) {Nature, xxii, 7(j). Mr. Murray of the Challenger found 
meteoric dust in the dredgings from the bottom of the sea. (See Archi- 
bald Geibie: Geol ,gical Sketches, ch. vi, Huniboldt Library, No. 39, p. 35.) Pro- 
fessor D. Kirkwood has reported a dnst-fall in Indiana, March 28, 1880 {Popu- 
lar Science Monthly, xvii, 553). 



12 



COSMICAL DUST. 




METEORS. 13 

An insignificant addition to the earth's mass, the reader 
may think. But let us examine. Ehrenberg states that the 
mass of dust which fell at Lyons in 1846, over an extent of 
400 square miles, was estimated by the French savans to 
be 7,200 quintals, or 793 tons. Chladni calculated that 
the aerolites enumerated by him as falling between 1790 
and 1818 weighed 600 quintals, and on this basis it has 
been held that the daily fall of atmospheric dust must be 
millions of quintals. Ehrenberg calculated that 243 quin- 
tals, or 27 tons, of red dust fell with snow over 100 square 
miles in the mountains about Salzbourg, on the 6th of 
February, 1862. According to M. Calvert, 15 French tons 
per square mile fell in Carniola on the 5th of April, 1869. 
Baron Nordenskjold says : " I estimate the quantity of 
the dust that was found on the ice north of Spitzber- 
gen, at 0.1 to 1 milligram per square metre, and probably 
the whole fall of dust for the year exceeded the latter fig- 
ure. But a milligram (.0188 grain) on every square metre 
of the earth amounts for the whole globe to five hundred 
million kilograms (say half a million tons)." 

Some of these estimates embrace, undoubtedly, dust 
transported from the Sahara. Let us then direct attention 
to unquestioned meteoric matter. It is said on good 
authority, that seven and one-half millions of meteors 
bright enough to be seen by the naked eye, pass through 
our atmosphere, on an average, every twenty-four hours, 
"and this number must be increased to four hundred 
millions if those be included which a telescope would 
reveal."* On special occasions they are seen to fall like 

*Schellen: Spectral Analysis, Am. ed. 404. Mr. Denning (Observatory, 
April 1883) states as a result of a rough computation, that about two hundred 
and sixty telescopic meteors appear hourly in a space fifty degrees square 
(using a ten-inch reflector and comet eye-piece), while the number of naked- 
eye meteors on the same space averages only twelve ; so that the proportion of 
telescopic and naked eye meteors is as twenty-two to one. Tf then we assume 
seven and one-half millions as the number of naked-eye meteors in the whole 



14 COSMICAL DUST. 

drops of rain in a brisk shower. Arago estimated that he 
saw two hundred and forty thousand in three hours, from 
his place of observation, on the 12th of November, 1833. 
My father, who witnessed this remarkable shower, has 
often described the spectacle which he beheld before day- 
light on that memorable morning, in such terms that it is 
easy to believe that hundreds of millions passed before his 
eyes within a space of one or two hours. The sky was 
woven into a network of fier}"^ fibres, and the snow on the 
ground glowed with a red illumination. Suppose each 
meteor to contain but ten grains of matter, if four hun- 
dred millions enter our atmosphere every twenty-four 
hours, this is two hundred and eighty-six tons daily, or 
one hundred and four thousand three hundred and fifty- 
two tons every year. In one hundred million years this 
amounts to ten million four hundred and thirty-five thou- 
sand two hundred millions of tons.* Now, while a few 
grains of matter in a state of intense incandescence may 
emit sufficient light to be visible at a distance of twenty 
to fifty miles, it is not probable that the average bolide of 
observation has a mass as low as ten grains. Thousands 
of them i^ossess too great a mass to be vaporized in the 
brief time spent in passing through the atmosphere; and 
then they reach the earth as meteorites, and constitute 
meteoric stones, aerolites and siderolites or meteoric iron. 
In this condition they have been found weighing several 
pounds, and occasionally several tons. In January, 1879, 
a meteoric body struck a house in Indiana, and in its 

sky in twenty-four hours, there should be one hundred and sixty -five million 
telescopic meteors in the same time. Mr. Denning"s estimates, however, arc 
far below the figures given by Schellen and here used. 

* Nevertheless this would produce a film only one-twelve hundred and fif- 
tieth of an inch thick over the whole earth. M. Dufour {Co?nj)fef: Rendus, Ixii, 
8401 has raised the question whether the addition of meteoric uuitter to the 
earth may not be the cause of the secular acceleration of the moon: but he has 
evidently exaggerated the importance of these additions. This acceleration 
moreover is otherwise explained. 



METEORS. 15 

descent to the cellar, passed through the body of a 
man in bed.* The intense and unequal heating of the 
exterior and interior portions of the larger meteorites is 
probably the cause of those occasional explosions which 
scatter brilliant fragments over areas miles in width, and 
send the report of a detonation to human ears. Many 
meteoric masses when found, present a surface smoothed 
and wrought into conchoidal depressions, and presenting, 
in many respects, the appearance of a mass of rapidly 
melting ice. Sometimes many distinct furrows have been 
sunken in the surface, showing the channels along which 
the liquefied j^ortions have been driven off behind, as the 
body shot through the air. 

Chemical analysis shows that meteorites are composed 
of well known terrestrial substances. The most abundant 
element is iron, but, in union with this, nickel always 
occurs, and sometimes, also cobalt, copper, tin and 
chromium. Other elements are silicon, oxygen, hydrogen, 
sulphur, phosphorus, carbon, aluminium, magnesium, cal- 
cium, sodium, potassium, manganese, titanium, lead, 
lithium and strontium. The silicon generally appears as 
silicates of various bases. Among the silicates, olivine is 
noteworthy as a greenish glassy mineral common in vol- 
canic rocks. Augite is another silicious mineral of similar 
terrestrial associations. 

Meteorites have been observed at calculated altitudes 
of forty-six to ninety-two miles. They move with veloci- 
ties ranging from fourteen miles to one hundred and 
seven miles a second. If we suppose a dark mass of 
matter moving at the rate of twenty-seven miles a second, 
to meet the earth, itself moving nineteen miles a second, 
and consider that the earth's attraction would develop an 

*This, according to the Indianapolis Journal, was Mr. Lconidas Grover 
"who resided in the vicinity of Newtown, Fountain county, near Covington, 
Indiana." 



16 COSMICAL DUST. 

additional velocity of six miles a second, we have an 
aggregate velocity of fifty-two miles a seco7id. With 
such a velocity, some of these meteorites plunge into our 
atmosphere. It hence becomes intelligible that even in 
the most rarefied portions of the atmosphere, the conden- 
sation in front of a meteorite moving with such velocity 
must develop sufficient heat to result in incandescence, 
and even in volatilization. Sir William Thomson deter- 
mined by experiment that a body moving through the air 
at the rate of one hundred and twenty-five feet per second, 
develops one degree of heat, and that with increased 
velocities, the increase of heat is proportional to the square 
of the velocity. From this principle it is easy to calculate 
that a velocity of four thousand feet per second would 
cause a heat of over one thousand degrees, and a velocity 
of forty-four miles per second would give a temperature 
of three or four million degrees. Long before any such 
temperature is actually reached, the substance of the 
meteoroid is dissipated in vapor. 

At the beginning of this century, it was generally be- 
lieved that aerolites were either condensations of vapors 
arising from the earth, or were projected from lunar vol- 
canoes. It has indeed been argued by Chladni,* by 
Halley,f and by Lichtenstein,J that aerolites are of cosmic 
origin; but this point was not clearly established until 
1833, when Professor Olmstead showed that the November 
meteorites of that year all radiated from one point in the 
constellation Leo, and could not, therefore, have partaken 
of the rotary motion of the earth. This conclusion was 
eagerly accepted by Poisson. Arago was the first to sug- 
gest § the periodicity of meteoric showers; but it required 

* Chladni : Ueber den Urspjning der von Pallas gefundenen und anderen 
Eisenmassen. 

t Halley, Phil. Trans., xxix, 161-3. 

$ Lichtenstein, Gottingen Taschenbuch. 

§ Arago, Annuaire, 1836, p. 297. 



METEORS. 17 

a third of a century more to attain to a clear conception 
of the theory of meteoric phenomena as now understood. 
It has been shown by the researches of H. A. Newton,* 
Schiaparelli, Le Verrier, Peters, Adams, Weiss, and others, 
that the meteors which fall within our atmosphere at regu- 
lar periods, in August and November, are derived from 
swarms of meteoric bodies revolving about the sun in 
orbits which intersect that of the earth. (See Figure 5.) 
The source of the August meteors is believed to be a cos- 
mical cloud forming a ring around the sun. The aphelion 
of this ring is 1,732 million miles beyond the orbit of Nep- 
tune. f The plane of the ring, or more properly, ellipse, is 
inclined at an angle of 64° 3' to the plane of the earth's 
orbit, and its orbital motion is contrary to that of the 
earth. The November shower occurs once in thirty-three 
years; and hence, though the meteoric orbit must intersect 
that of the earth, so that the earth" passes it annually, the 
meteors do not stretch in a continuous ring around their 
orbit. From the fact that the meteoric belt is intercepted 
by the earth only once in thirty-three years, it was shown 
by Professor Newton that in 33^ years the swarm must 
make one revolution, or 32^, 34^, 65^ or 674- revolutions; 
and that, to test which of these is the correct number, we 
must investigate the possible influence of the several 
planets upon the movements of the swarm. The investi- 
gation was made by Schiaparelli of Milan, and about the 
same time, by Professor Adams of England; and it was 
thus demonstrated that the 33:^ years period is the only 
one which satisfies all the conditions.:}: On this theory of 

* See Professor Newton's remarkable succession of contributions to our 
knowledge of the phenomena of meteorites, and his sagacious discussions of 
these phenomena, and inferences from them, in the successive volumes of the 
American Journal of Science^ from 1861 to 1873. 

i This is based on Oppolzer's determination of a period of 124 years, and is 
obtained by Kepler's third law. But the period is not accurately known. 

• X Sir William Thompson. Address at Edinboro Meeting British Association, 
Arner. Jour. Sci., Ill, ii, 289, Oct. 1871. 
2 



18 COSMICAL DUST. 

the orbital period of the meteoric cloud, it is apparent 
that it stretches for a long distance along its orbit, since 
it is intercepted by the earth on the two Novembers fol- 
lowing the principal shower,, though the meteoric fall is 
greatly diminished at the second and third intersections. 
Assuming the meteoric period to be thirty-three years, the 
cosmic cloud must therefore stretch over one-eleventh of 
the whole orbit. The motion of this cloud is also retro- 
grade; the inclination of the orbit is 14° 41', and its 
major axis is ten and one-third times the mean diameter of 
the earth's orbit. The node or point of intersection with 
the earth's orbit has a motion of 52". 4 annually in the 
direction of the meteoroidal motion. This meteoric orbit 
is therefore, like the other, similar to that of a comet; and, 
if it were less inclined to the ecliptic, would probably 
serve as a source of meteoric showers to Mars and the 
x\steroids. 

The relations of these two principal meteoroidal orbits 
to the solar system are intended to be illustrated bj' the 
diagram. Figure 5. The orbits of the earth, Jupiter, 
Saturn, Uranus and Xeptune are here supposed to lie in 
one plane, and are so situated that the eye takes a per- 
spective view across the plane. The relative magnitudes 
of the orbits are not accurately represented, and Neptune's 
orbit is shown only in very small part. The eartli's orbit 
is so placed that the major axis does not correspond with 
the longest dimensions shown in the perspective. The 
same is true of t?he other orbits. The extremities of the 
earth's major axis show approximately the positions of the 
earth at the solstices, June 21st and December 21st. The 
arrows show the directions of the motions represented in 
the diagram. 

The orbit of the November swarm of meteoroids is 
shown as having an angle of 14" 41' with the plane of the 
Earth's orbit. The greater part of this orbit lies below the 



METEORS. 



19 




Fig. 5. Illustrating the Positions of the August and November 
Meteoroidal Swarms. 



20 COSMIC A L DUST. 

plane of the ecliptic. The motion of the swarm is nearly 
opposed to the Earth's motion. The swarm reaches its peri- 
helion a little before it crosses the Earth's orbit on Novem- 
ber 14. The Earth passes on, after the crossing, to the 
\vinter solstice and beyond. The train, meantime, is trail- 
ing across the path of the Earth at the November point. 
It is of such length that it continues to trail across until 
the Earth has reached the November point again and 
again. It is, therefore, many millions of miles in length. 
The aphelion point of this meteoroidal orbit is a little more 
remote than the orbit of Uranus. 

Similar]}^, the orbit of the August swarm of meteor- 
oids is represented as having an angle of 6-4° 3' with the 
plane of the Earth's orbit. It is, therefore, turned up so 
that the view presented in the figure is much less oblique, 
and the orbit appears very broad. The longer axis of the 
orbit, however, is greatly foreshortened, and the two 
branches must be conceived as retreating into the far 
distance, a little to the left of the direction of the line of 
sight. The aphelion, which is one thousand seven hun- 
dred and thirt^'-two million miles beyond the orbit of 
Neptune, is almost included in the diagram. This swarm 
is lour million miles broad, and reaches quite around its 
orbit, though the meteoroidal bodies are not uniformly 
distributed. Hence the August shower is of annual 
occurrence, while the brilliancy of the display is very 
variable. 

Several other remarkable cosmic clouds have been recog- 
nized, and the following table of the best established has 
been arranged from the Aniuiaire da Bureau des Lonrji- 
tudes for 1881. The table gives the epoch, right ascen- 
sion and declination of the principal radiant point in each 
cloud. 



METEOKS. 



21 



TABLE OF METEOROIDAL SWARMS. 





« 


Radiant Points. 


Epochs. 


I. 


II. 


III. , IV. 




R.A 

238° 

273° 

267° 

342° 

43° 

74° 

148° 

25° 

105° 


Dec. 


R.A 


Dec. 


R.A 

225° 

294° 
112° 
279° 


Dec. 

+52° 

+52° 
+29° 
+56° 


R.A 

204° 
9° 


Dee. 


I 

II 

III 

IV 

V 

VI 

VII 

VIII 

IX 


Jan. 2 to 3 

Apr. 12 to 13 

Apr. 19 to 23.... 
July 26 to 29 ... . 
Aug. 9 to 14 ... . 
Oct. 19 to 25 ... . 
Xov. 13 to 14. . . 
Nov. 27 1o29 ... 
Dee. 6 to 13 


+45° 
+25° 
+35° 
-34° 

+57° 
+25° 
+24° 
+45° 
+30° 


238° 

345° 
95° 
53° 

149° 


-30° 

+50° 

+15° 
+32° 

+41° 


-18° 
-19° 



Notes. Swarm II is perhaps only a stray portion of III. Of 
the latter the Chinese records mention many recurrences, and the 
swarm is thought connected with the Comet I 1860. Swarm IV is 
spi-ead over the whole heaven of the northern hemisphere, but in 
the southern, the principal radiant is as indicated. Swarm V is 
known as the Swarm of St. Lawrence, also as Perseids. Accord- 
ing to J. J. Schmidt, there are not less than forty radiant points in 
all. These meteors are connected with the Comet III 1862. Swarm 

VI has many radiants indicated in the course of many years. Swarm 

VII is known as the Leonids, which revolve in the orbit of the 
Comet I 1866. Swarm VIII is in connection with the Comet of 
Biela-Gambart, which in 1872 gave origin to a fine display of mete- 
ors. Swarm IX is composed of small bodies, but exceptionally brill- 
iant. It possesses numerous radiant points. 



Here arc given the positions of twenty important radi- 
ant points, each of which may really appertain to «a distinct 
swarm, though exhibited simultaneously with other radi- 
ants. But besides these are numerous others; and if each 
separate radiant corresponds to a distinct swarm, moving 
in a distinct orbit, we hftve knowledge of more than a hun- 
dred meteoroidal orbits which pass in close proximity to 
the earth's orbit. This, in the opinion of some physicists, 



22 COSMICAL DUST. 

is the fact. In truth, there is scarcely a nio-ht in the year, 
as every one can testify, when some meteors may not be 
seen. If these bodies are generally connected with swarms, 
large or small, there is scarcely a night when the earth's 
path is not intercepted or grazed h\ a meteoroidal train. 
A similar number must pass during the day; and we 
should thus haye indications of over seven hundred passing 
annually in close proximity to the earth, each of which 
might be 794,000 miles in diameter. These trains are as 
clouds of sand floating in space, but describing regular 
orbits about the sun. The constituent bodies may be 
conceived as possessing all dimensions, from a molecule 
of matter to the size of an asteroid. 

Now, let it be borne in mind that the cosmic clouds of 
whose existence we have learned, are only such as have 
orbits intersecting or grazing that of the earth. Let it be 
remembered, too, that of all meteoroidal orbits intersecting 
that of the earth, only such can be revealed as are traversed 
by the meteoroidal swarm, at the point of intersection, at 
the same time that the earth happens to be passing the 
same point. How man}^ must there be located in such po- 
sitions as not to be brushed by the earth's atmosphere, or 
impressed by the earth's attraction. Tlie intersection of 
one of these meteoroidal orbits by that of the earth is al- 
most like striking a solitary line by a random shot in infi- 
nite space. The interception of a swarm is like hitting a 
particular point. Millions of chances against it. How 
many meteor swarms have we a right to assume as proba- 
bly sweeping in all conceivable directions at all conceivable 
distances, within at least the limits of our system, about 
this central sun? Could our vision be unsealed, we should 
behold the infinite firmament dotted with meteors hurrying 
to and fro, as snow-flakes in the ■wildest wintry storm. 

From this survey of facts and theories it appears mani- 
fest that the "dust of time'" comes down to us out of the 



ZODIACAL LIGHT. 23 

interplanetary spaces. These meteoric matters are samples 
of the stuff which exists in the far regions where the stars 
are shining. It comes to us and we handle it and investi- 
gate it, and find it exactly like the stuff from which our 
world is made. We are not isolated, as we had thought, 
from the starry realm. Even the meteors are messengers — 
flaming messengers — bringing us these tidings from dis- 
tant provinces, and assuring us that the government whose 
details are administered upon our earth is loyally recog- 
nized in the regions lying on the distant verge of the visi- 
ble universe. 

§ 2. THE ZODIACAL LIGHT. 

Secondly, the Zodiacal Light yields evidence of cos- 
mical matter floating in space. This is a faint yellowish 
light which rises like an ill-defined cone from the western 
horizon just after sun-set during winter and spring, and 
from the eastern horizon just before sun-rise in summer 
and autumn. It extends very nearly in the plane of the 
ecliptic; and hence, when the direction of the ecliptic is 
strongly inclined toward the horizon, this faint light is 
obscured by the atmosphere, and remains unnoticed. It 
sometimes extends nearly to the zenith, and there are 
many accounts of its appearance, especially in tropical 
latitudes, in the western and eastern horizons, at the same 
time,* though the brightness is much less in the horizon 
opposite the sun. 

Polariscopic study of the light shows it to be polarized 

*For a valuable mass of observations ou tbe zodiacal light, with a large 
number of graphical illustrations, see Chaplain George Jones' memoir in Rej)ort 
IT. S. Japan Expedition, vol. iii, as also a brief statement in Astronomical Jour- 
nal No. 84, and Amer. Jour. ScL, If, xx, 138-9. For other data see M. Houzeau's 
memoir in Astrononiische Nachrichten, 1843, and the valuable paper of Prof D. 
Olmsted in Am. Jour. Set., IT, xii, 309-22, embracing the best graphical delinea- 
tion known to the present writer. For historical and critical notes see Hum- 
boldt ; Cosmos, Otte translation, i, 137-44. 



24 COSMICAL DUST. 

in a plane passing through the sun. The amount of 
polarization is 15 to 20 per cent. This result shows that 
the light is derived from the sun, and is reflected from 
solid matter consisting of small bodies apparently not 
differing in their nature from terrestrial minerals.* Spec- 
troscopic study of the light leads to the same conclusion. 
Its spectrum is continuous, and is sensibly the same as 
that of faint sunlight or twilight. f It seems well settled, 
therefore, that we have in this phenomenon a true exam- 
ple of cosmical dust floating in space and rendered lumi- 
nous, like the dust rising from our streets, by the reflection 
of solar light. This happens to be very exactly the same 
view promulgated by Dominicus Cassini in 1730, who was 
the first to devote elaborate study to this phenomenon. 

The arrangement of these cosmical matters in relation 
to the sun and the earth has been much discussed. La- 
place concluded that they could not belong to the atmos- 
phere of the sun, since the form is far too lenticular for a 
body rotating no more rapidly than the sun. ^ Still, he 
suggests, as Cassini had done at an earlier date, that the 
matter of the zodiacal light may surround the sun as a 
ring; and he suggests, also, an origin for it, in conformity 

* A. W. Wrip:ht, Am. Jour. Sci., Ill, vii, 451-9. 

t A. W. Wright, Am. Jour. Sci., Ill, viii, 39-46. Some other observers, nota- 
bly MM. Respighi and Angstrom, have reported a bright yellow line in the spec- 
trum; but Prof. Wright found it present only when the aurora borealis was 
displayed, and was never seen when the aurora was absent. Father Secchi's 
experience was the same. See, also, observations by Prof. Pia/zi Smyth, 
Monthly Notices, Boy. Astr. Soc, June 1872, p. 277, and M. Liais, Comptes Ren- 
dus, Ixxiv, 262, 1872. See further, R. A. Proctor, Monthly Notices, xxxi, No. i, 
Nov. 11, 1870. 

t Laplace: Systeme du Monde, Liv. iv, ch. x, ed. 18;24, p. 270. Nevertheless 
Father Secchi says, in view of the changes in the color of the zodiacal light, at 
the time of perihelion passage of the comet of 1843, '' cela prouverait done que 
cette lumiere n'est que Tatniosphere solaire, et non pas un anneau d(?tache'"(-^ 
SoUil, 2d ed., ii, 433). It is generally represented that Kepler had thought the 
zodiacal light to be a portion of the sun's atmosphere, but Humboldt maintains 
(Cosmos, i, 140, note) that this "limbus circa solem, coma lucida''' has no refer- 
ence to this phenomenon. 



ZODIACAL LIGHT. 25 

with his celebrated hypothesis respecting the origin of the 
planets. " If," he says, "in the zones abandoned by the 
atmosphere of the sun, there existed any molecules too 
volatile to unite with each other or with the planets, they 
ought, in continuing to circulate about that body, to pre- 
sent all the appearances of the zodiacal light, without 
offering any sensible resistance to the various bodies of 
the planetary system, for the reason either of their ex- 
treme tenuity, or because their motion is almost exactly 
the same as that of the planets which encounter them." * 

Whether this is a correct conception of the zodiacal 
light or not, it is generally agreed that the phenomenon 
arises from a ring of meteoroidal bodies encircling the sun, 
nearly in the plane of the ecliptic, and probably rotating 
like the rings of Saturn. But considering that the phe- 
nomenon has so frequently been witnessed in the east and 
west at the same time, it is necessary to assume that while 
most of the matter lies within the earth's orbit, some por- 
tion extends beyond that limit. Accordingly, the earth 
moves within the assemblage of particles. Consequently, 
unless they have precisely the same velocity as the earth, 
they must by their collisions offer a resistance to the 
earth's motion. The entrance, then, of these zodiacal 
molecules into the earth's atmosphere might present me- 
teoric phenomena. 

A different location of this annulus is maintained by 
others. Rev. George Jones, before cited, argues that the 
appearance of the light in both horizons at the same time 
is evidence that the annulus surrounds the earth. Profes- 
sor Stephen Alexander f for similar reasons rejects all 
heliocentric theories, and maintains that the annulus is an 

* Laplace: Systhne du Monde, Note vii, 415-6. M. Roche also regards the 
matter of the zodiacal light as a remnant of the primitive nebula. 

tS, Alexander, Smilhso7uan Contributions, xxi, No. i, 68. In opposition to 
the geocentric theory see F. A. P. Barnard, Am. Jour. Set., II, xxi, 21T-.S7; and 
Commander Charles Wilkes, Pi'OC. Amer. Assoc. 1857, 83-92, 399-401. 



26 COSMICAL DUST. 

appurtenance of the earth, lying nearl\" in the plane of 
the moon's orbit, and that it is girdle-shaped instead of 
discoid. He calls it " a nebulous girdle revolving around 
the earth in the same time and general direction with the 
moon." He compares it, like Chaplain Jones, with the 
dusky ring of Saturn, though diifering in shape. The very 
unequal intensity of the light in the horizon opposite the 
sun is a fact at variance with the geocentric theory. The 
original conception of Cassini and Laplace seems most 
conformable with all the facts; and there is much reason 
in the supposition also, that this ring is a remnant of the 
primitive nebula, detached according to the principles 
which I shall hereafter explain. One circumstance, how- 
ever, indicates that this phenomenon may be something of 
modern origin; since, of all the acute observers of the 
heavens in ages past, from the Babylonians to Tycho and 
Kepler, none make any allusion to it before the latter part 
of the seventeenth century, Childrey, in 1G61, gives the 
first clear and unmistakable mention of it.* If it is 
indeed, a plienomenon of modern origin, it cannot, of 
course, be viewed as a vestige of the work of planetary 
evolution. We must seek for some appropriate existing 
action and process, and we may direct our inquiries to the 
seemingly repulsive power exerted by the sun in the 
radiant forms of the solar corona and in the tails of 
comets, f 

*Childrey: Britannia Baconica, 183, cited by Humboldt. 

tit may be mentioned a? a matter of interest that Pro.f. D. Olmsted as 
early as 18:34 {Am. Jour. Sci.) sugge^^ted a nebulous body revolving around the 
sun as the source of the November meteor shower of 18^33, and he identified 
this with the zodiacal light in 1851 in the memoir before cited. The same 
suggestion was made in 1836 by M. Biot as to the nebular origin of the meteors. 
Commander Wilkes (ojJ. oil., p. 89) concludes that the zodiacal light "is the 
result of the illumination of that jxtrtiou or section of the earth's atmosphere 
on which the rays of the sun fall perpendicularly." 



COMETS 27 

§ 3. COMETS. 

Thirdly, the Comets are now known to be simply con- 
glomerations of cosmical dust. These bodies are not, as 
Kant and others have supposed, natives of our system. 
This is apparent when we consider that their motions, save 
the fundamental principle of motion in a conic section, 
bear no conformity to the rule of motions of the planets and 
satellites. Comets approach the sun from all conceivable 
directions, moving sometimes nearly in the plane of the 
ecliptic, sometimes plunging down from the neighborhood 
of the zenith or rising from the nadir or emerging into 
visibility in the vicinity of either pole. From a table of 
300 comets recently published by Niesten,* it appears that 
in regard to the inclinations of their orbits 67 ranged be- 
tween and 30°; 113 between 30° and 60°, and 110 
between 60° and 90°. Comets move accordingly in all 
directions around the sun. About half of all the comets 
known possess a retrograde motion; though most of the 
comets of short period possess direct motion — a circum- 
stance which, as will be shown, seems to be due to the 
perturbative influence of planets moving in a common di- 
rection from west to east. That they are foreigners in our 
system is apparent, also, from the fact that only a small 
portion of the comets which visit us are known to move in 
elliptical orbits. That is, the great majority never return 
to describe another circuit about our sun. They approach 
from unknown regions, and retire to regions equally un- 
known. It is further apparent from the non-conformitv 
of comets to the chemical constitution of the sun and 
planets. We only know that carbon, apparently combined 
with hydrogen, exists in the substance of some of them. 
It may be considered, however, very doubtful whether we 

*>siesten: Tab'e ties Cometes, in Annuaire de I'Observatoire Royal de 
Bruxelles. 



88 COSMTCAL DUST. 

are in a position to affirm or deny the presence of any 
element. 

Of the thirty-eight comets, believed to revolve in ellip- 
tic orbits, only twelve have been seen at more than one 
return. 

The following is a list of the principal comets of short 
period. Those marked with a star have been seen at more 
than one return: 

COMETS OF SHOET PERIOD. 

Period 
Motion. yrs. 

* 1. Encke's (Pons, 1818) Direct 3.288 

'2. Blanpain's (1819) Direct 4.81 

3. Burkhanlt's * (1766 11) Direct 5.025 

* 4. Temper^ (1873 II) Direct 5.066 

5. De Vico's (1844 1) Direct 5.459 

* 6. Brorsen's (1846 III) Direct 5.473 

* 7. Winnecke's (1858 II) Direct 5.727 

8. Pigott's(1783) Direct 5.888 

* 9. Tempers (1867 II) Direct 5.965 

* 10. Swift's (1880 r\^) Direct ?6. 

* 11. Biela's f (Feb. 1826) Direct 6.619 

* 12. D'Arrest's (June 27, 1^51) Direct 6.664 

* 13. Faye's (Nov. 22, 1843) Direct 7.412 

* 14. Denniui^'s (F. Oct. 4, 1881) Direct 8.8567 

15. Peter's (1846 V) ? Direct 12.85 

* 16. Tuttle's (Jan. 4, 1858) Direct 13.81 

1 7. Tempers (1866 I. 'Comet of Xov.Meteors") Retrogratle 33.18 

18. Stephan's (1867 I) Direct 33.62 

19. Westphal's (.Inly 24. 1852) Direct 60.03 

20. Pons' f.July 20. 1812) Direct 70.69 

21. De Vico's (1846 III) Direct 73.25 

22. Gibers' (March 6, 1815) Direct 74.05 

23. Brorsen's (1847 V) Direct 74.97 

* 24. Halley's Retrograde 76.30 

25. (1862 III, "Comet of Aug.Meteors") Retrograde ? 124. 

* Thought perhaps^ identical vith Winnecke's. 

+ Xot seen since 1852. Supposed to have struck the earth at the end of 
November, 1872, and to have caused the memorable meteoric display at that 
date. This is Swarm viii of the preceding Table. 



COMETS. 29 

It has been conjectured that the great southern comet, 
I 1880, is the same as the great comet of 1843.* Donati's 
comet of 1858 has a calculated period of 2,100 years; the 
comet of 1811 and the great comet, B 1881, periods of 
3,000 years; that of 1G80 is expected to be absent 8,814 
years. Coggia's comet, IV 1874, has, according to Dr. 
Hepperger, a period of 13,708 years, while the comet of 
July, 1844, has a calculated period of 100,000 years. 
These long periods, however, are exceedingly uncertain. 
The elliptic character, even, of the orbits, is not in all cases 
fully established. Even when really elliptic, moderate 
perturbations may cause great change in the periods. 

The relative position of the great comet of 1881t is 
shown in perspective in Figure 5. The point of view is 
such that the plane of the cometary orbit is presented 
quite obliquely, and the spectator contemplates it from 
below. The reader must therefore conceive the lower 
branch of the orbit much more remote than the upper. 
P, below the ecliptic, denotes the perihelion point of the 
comet, and N, the node where it passed from the south to 
the north side of the ecliptic. This diagram explains why 
the comet was discovered in May in the southern hemi- 
sphere, but was not seen in the northern hemisphere till 
four weeks later. In May it was below the horizon of 
northern observers; and later, when it had risen above 
their horizon, it was too nearly in the direction of the sun 
to be seen. Meantime it passed its perihelion, and when 
first seen, June 20, in the northern hemisphere, it was 
already receding from the earth and the sun. The dia- 
gram explains, also, why northern observers saw this 
comet in the neighborhood of the north star, or the region 

* Swift: Science WibS. 

+ Comet B 1881, discovered by Tebbutt in New South Wales, May 22, and 
rediscovered in the northern hemisphere, June *0, by G. W. Simmons, then at 
Morales, Mexico. See an illustrated article About Comeishy A. N. Skinner in 
Popular Science Monthly, xix, 790-5, Oct., 1881. 



30 COSMICAL DUST. 

toward which the axis of the earth is directed ; and why it 
continued in that neighborhood as it receded during July, 
though slowly diverging from the direction of the polar 
star. The diagram also shows why this gradual diver- 
gence was to an observer in the evening, toward the left 
from the pole, in the direction of the sun. This comet 
remained visible for seven months, and could be faintly 
seen as late as Christmas, 1881. It was then in the con- 
stellation Cepheus. It was even visible telescopically one 
or two months later. The great comet of 1882 will not be 
forgotten by the present generation. It was first seen 
September 2, and continued visible to May 6, 1883, pass- 
ing over 339^° of heliocentric arc, leaving but 20^° to be 
completed during the remainder of its orbital circuit, sup- 
posing it to be periodic. The great comet of 1680 was 
visible through 345° of arc, from November 14, 1680 to 
March 19, 1681. 

The great comet, 1882 ^, just mentioned, is worthy of 
more particular notice. It was seen at Auckland, N. Z., 
September 2, 1882 ; at the Cape of Good Hope, by Finlay, 
September 6, and at Rio, by Criils, September 12. In 
approaching perihelion, it was seen by Finlay and others 
to pass before the sun's disc, though wholly invisible 
during the transit. After perihelion, the nucleus was seen 
to begin to divide, as early as September 28.* On Octo- 
ber 5, two nuclear fragments were seen at Strasbourg. 
Three fragments were reported at the same date by Bar- 
nard at Nashville, Tennessee, and Wilson, at Cincinnati; 
while from Guatemala five distinct bodies were reported. f 
By October 12, four separate condensations were distinctly 
seen. ^ On October 14, Mr. E. E. Barnard, of Nashville, 

* Nature, xxvii, 150, with views for September 16 and October .'JO. xVlso note, 
ibid, 161. 

\ Nature, xxvii, 113. 

:|:W. Doberck, iU Markree Observatory. {Nature, xxvii, 129. with ilhistra- 
tions.) ES. Holden saw at Madison, Wis., three condensations {Amer. Jour. 
Sci., Ill, xxiv, 435, Nature, xxvii, 246). 



COMETS. 31 

found, to the south of the comet, "a large distinct comet- 
ary mass fully 15' in diameter, and a similar, but less 
bright object close behind this, their borders touching, 
and on the opposite side of the first, a third fainter 
mass. The three were almost in a line east and west. 
More of these cometary masses were found toward the 
south-east. There were at least six or eight within about 
6° south by west from the head of the great comet." 
They were not afterward seen.* Dr. Schmidt, of Athens, 
had reported a detached cometary mass at an earlier date.f 
On January 27, Mr. Ainslie Common, of Ealing, "saw the 
nuclear part of the comet larger but less bright than pre- 
viously, and resolved into a string of brightish points, the 
second and third of which were much the brightest." A 
sketch by Mr. Common showed five points of condensa- 
tion. X The separation of the nucleus seems to have con- 
tinued as long as the comet remained under observation. 
These facts are significant, and appear to have an important 
bearing on the genetic connection of comets and meteors. 
The calculations of Chandler give this comet an orbit of 
4,070 years with retrograde motion. According to Frisby, 
its period is 794 years ; according to Kreutz, 843 years ; 
according to Morrison, 652^ years. § A. S. Atkinson, of 
Nelson, N. Z., reports it visible to the naked eye as late as 
February 28, 1883, and with telescopes, until May 6. || 

Comets generally present a nucleus, a coma of diffused 
light surrounding the inicleus, and a long tail, generally 
turned away from the sun, somewhat curved backwards, 
and having a well-defined anterior border, while the pos- 

* Nature, xxvii, 400. 

\ AstronoDiUcJie Nachrichten, No. 2,468, Natvre, xxvii, 20-1. 

X Nature, xxvii, 400. Something quite s^imilar had been observed Nov. 15.7 
by W. C. Winlock at Washington. {Nature, xxvii, 129, figure.) 

% Nature, xxvii. ,300. 

I Nature, xxviii, 225, July 5. 1883. On this comet see the important lecture 
of Prof. Schiaparelli, reported in Nature, xxvii, 533-4. 



32 COSMIC A L DUST. 

terior border gradually fades off into space. The tenuity 
of all parts of the comet is such that stars of the tenth 
and eleventh magnitudes have been seen, not only through 
the expanded portion of the tail, but through the most 
condensed portion, and even through the nucleus itself. 
From these facts it is apparent that the amount of matter 
in a comet is generally inconsiderable. This is demon- 
strated by the fact that the comet of 1776 passed amongst 
the satellites of Jupiter without causing the slightest dis- 
turbance in their motions. The comet, on the contrary, 
was thrown into a totally different orbit. Similarly, the 
comet of 1861 actually came into contact with the earth 
on the 30th of June of that year, and the human race was 
not annihilated. Indeed, the only indication of the start- 
ling event was a peculiar phosphorescence of the atmos- 
phere. According to the accepted relation between 
comets and periodic meteor showers, it may be said the 
earth comes in contact with a comet on every occasion 
of such displays. 

In connection with the evidences of the extreme tenuity 
of comets, may be mentioned the parting of Biela's comet 
while actually under observation, in 1845. On the 26th of 
November, it was a faint nebulous spot, not perfectly 
round, and with an increased central density. On the 
19th of December it was more elongated; on the 29th, it 
had parted. For three months the twin comets were traced 
with a gradually widening interval between them. Thus 
they departed from view on their appointedjourney of 6f 
years. At the end of that period, in August, 1852, the 
twin comets reappeared, but with an interval increased 
from 154,000 miles to 1,404,000 miles. The pair were ex- 
pected again in 1859 and 1866; but since 1852 they have 
never put in an appearance. Some planet has turned them 
into an orbit so changed as to be unidentifiable, or their 
substance has passed into some other condition of exist- 



COMETS. 33 

ence. The nucleus of the great comet of 1882 exhibited 
a distinct tendency to separate into three or four parts. 
It remained visible till the early months of 1883, still re- 
vealing a state of incipient division. 

To what other condition of existence is it possible for 
cometary matter to pass ? According to Schiaparelli and 
Oppolzer, the meteoric ring, or partial ring, is only a de- 
generated comet. They suppose a train of meteoroids 
follows in the path of the comet, and that this becomes 
continually more elongated until the head overtakes it. 
Comet No. Ill, of 1862, has an orbit calculated by Oppol- 
zer, which is almost identical with the orbit of the meteoric 
ring that yields the shooting stars of the 10th of August, 
as calculated previously by Schiaparelli. This comet then, 
Schiaparelli concludes, is merely the remains of the origi- 
nal comet out of which the meteoric ring was formed. In 
other words, the comet and the meteoric ring are one and 
the same thing. This ring has a major diameter of 10,948 
millions of miles; and at the place where the earth trav- 
erses it on the 10th of August, it must have a thickness 
of 385,800 miles, since the meteoric display continues six 
hours, and the earth travels in August at the rate of 18 
miles in a second. The ring reveals itself as a comet only 
when its nuclear portion happens to be seen near the node 
when the earth passes. This happens once in about one 
hundred and twenty years. 

By similar calculations, it has been shown that the No- 
vember meteoric ring, or partial ring, is identical with 
Tempel's comet, or No. I of 1866. This comet, according 
to the calculations of Le Verrier, entered our system in 
the year 126 A.D., passing so near the planet Uranus as 
to be thrown into an elliptic orbit having a period of 
thirty-three years.* In consequence of having its perihe- 

*This conclusion is rejected by Schiaparelli, in consequence of the alleged 
insufficiency of the mass. {Les Mondes, xiii, 501, March 28, 1867. ) 
3 



34 COSMICAL DUST. 

lion at nearly the same point as the earth, it becomes the 
source of the November meteoric showers, which occur at 
intervals of thirty-three years. 

The lost comet of Biela is thought to reveal itself in a 
train of meteoroids which was intercepted by the earth 
November 27, 1872. 

As to the physical condition of these cometary groups 
of cosmical atoms, it appears from spectroscopic observa- 
tions, that the coma and tail are luminous only by reflected 
light, like the zodiacal ring; but the nucleus is proved to 
be self-luminous, either as an incandescent solid or liquid. 
But it must not be considered as a continuous solid or 
liquid, since its tenuity is far too great. The condition of 
the nucleus then may be comparable to that of the cloud 
of heated particles in the flame of a lamp, or that of a 
mist of molten particles; while the tail may be compared 
to a cloud of dust illuminated by the rays of the sun. 

That some physical relation exists between comets and 
meteors seems intelligible and entirely probable. The 
nature of that relation, as generally conceived, is such as 
has been stated. Undoubtedly the comets revealed to our 
vision have had a long previous course of development. 
Tliere seems, at first, reason for supposing that the meteor- 
oidal stage is an earlier rather than a later phase in come- 
tary life. But reflection renders it probable that the 
regions of cometary evolution lie beyond the limits of a 
planetary system. In the midst of such a system, the 
perturbative influences, to which cometary aggregations 
are so susceptible, must inevitably be of a destructive 
rather than a constructive character. But I reserve the 
fuller expression of my own conclusions until after atten- 
tion has been directed to nebular phenomena, and the col- 
lateral indications of a vast stock of world stuff dissemi- 
nated through infinite space. 



NEBULA. 35 

§ 4. SATURNIAN RINGS. 

Fourthly, the Saturnian Rixgs afford another exam- 
ple of cosmical dust. These have been shown by Profes- 
sor Peirce to be neither continuously solid nor liquid. 
This is also apparent from tlie inconstancy in the number 
and aspects of the rings, and the great tenuity of the 
marginal zone of one of them. The matter of these rings 
must then be regarded as consisting of particles of solid 
dust. They have, therefore, the constitution of a comet's 
tail, and reflect solar light similarly. They are identical 
with the meteoric rings, save that the constituent parti- 
cles are more closely crowded, and thus reflect sufficient 
light to become visible. 

It is quite supposable that the zone of the asteroids, of 
which more than two hundred are now known to attain 
the size of small planets, is merely another meteoric ring. 
It is the opinion of some astronomers that the number of 
asteroids amounts to millions.* This supposition, however, 
respecting the nature of the asteroidal group is not enter- 
tained by the present writer. 

§ 5. NEBULA. 

Fifthly, the Nebul.e are other and remoter examples of 
cosmical dust, and are every way full of interest and sug- 
gestiveness. These mysterious assemblages of matter de- 
mand our most serious attention. They reveal themselves 
as faint clouds of luminosity lying against the dark blue 
sky. When Sir William Herschel, with his forty-feet 
reflector, first brought the nebuLe into prominent notice, f 
he found that many of them resolved themselves into dis- 
tinct points of light under the higher powers of his instru- 
ment. A nebula, therefore, seemed to be an assemblage 

*Tlie 228th at^teroid was discovered by Palisa, August 19, 1882. 

t It is said tliat most of his work was done with the twenty- feet rellector. 



36 COSMICAL DUST. 

of thousands of stars, so far removed as to be brought by 
perspective into apparent close proximity. These he re- 
garded as other firmaments, removed incalculable distances 
beyond the outer limits of our own firmanent of stars, and 
having a life probably the counterpart of our own firma- 
mental life. But while thousands of the nebuLne were 
thus resolvable, other thousands resisted the higher pow- 
ers of his instrument, which is said to have magnified up 
to six thousand diameters. The irresolvable nebulas Sir 
William Herschel conceived to be crude world-stuff, out of 
which suns and planets were destined to be made. This 
idea, so consonant with the previous suggestion of Kant, 
was taken up by Laplace, and put into the shape of a 
physical theory, which became known as the "nebular 
hypothesis." * 

With the introduction of the gigantic reflecting tele- 
scope of Lord Rosse, fifty-two feet in length, many of the 
nebulae w^ere resolved which Sir William Herschel had re- 
garded irresolvable ; and many hitherto unseen nebulas 
were brought within the range of vision. It appeared, 
therefore, that the outer limits of the material creation 
had not been reached, and the suspicion was aroused that 
all nebulcTe might be resolved if we could apply unlimited 
telescopic power. This idea was antagonistic to the nebu- 
lar hypothesis, and the latter accordingly receded in favor. 

As the power of the telescope to reveal the constitution 
of the nebulas seemed to have reached its limit, and the 
prevailing conviction was only a presumption that all 
nebulae are inherently discrete or cluster-like, we are in- 
debted to the spectroscope for any further advance of 
knowledge in this direction. 

* Laplace, however, does not seem to have been acquainted with Kant's 
older and most suggestive speculations; but he acknowledges his indebtedness 
to Sir William Herschel, in bringing to light the actual existence of the crude 
world-material which furnished the starting point of Laplace's speculation. 
The reader will find a summary of opinions in Part IV of the present work. 



NEBULiE. 37 

The spectroscope, invented by Bunsen and Kirchoff in 
recent times, is one of the most marvellously efficient in- 
struments for scientific research that has ever been devised. 
Its powers are magical. It seizes the slender ray admitted 
to a darkened room through a narrow slit in the window 
shutter, and extorts from it the confession of the nature of 
its origin. It compels the ray to write out the names of 
the substances which enter into the constitution of the 
luminous body from which it proceeds. It compels it to 
declare whether its source exists as a luminous gas or 
vapor, or as an incandescent solid or liquid, or as a glow- 
ing solid or liquid shining through gases or vapors. Such 
revelations of the constitution and physical condition of 
suns and stars and nebulae are not alone surprising; they 
are amazing. A luminous body separated from us by 
hundreds of millions of miles, sending its light across 
unexplored intervals of cold space, so remote that the 
light which falls upon our eyes to-night must have left its 
source before Shufu reared the great pyramid above the 
plains of Egypt, has indited a message which we read in 
the laboratory, like a letter delivered by post from a friend 
in another city. 

And yet this, like other magic, is simple when ex- 
plained. It all depends on the undulatory origin of light, 
and the inequality of the waves for the different colors of 
which white light is composed. Every one understands 
that a ray of light passed through an angle of a prism is 
decomposed into seven colors commonly called "primary," 
which range themselves in a fixed order on a screen. The 
decomposition of the white ray results from the varying 
refrangibility of the constituent colors. The different 
refrangibilities result from the different wave-lengths of 
different colors. The length of a luminous wave varies 
from about seven hundred and sixty millionths of a milli- 
meter at the red end of the spectrum to about three hun- 



38 COSMICAL DUST. 

dred and ninety-three millionths of a millimeter at the violet 
end.* That is, the force which is the cause of the sensa- 
tion of light produces inconceivably minute undulations in 
some medium — generally regarded the same as the ethereal 
medium — and these undulations are propagated at the 
rate of about one hundred and eighty-five thousand miles 
a second, entering the eye and striking the retina, and 
thus being followed by the sensation of light. When the 
undulations are of such width that only three hundred and 
ninety-five trillions of them enter the eye in a second, we 
experience the sensation of red light; when they are so 
minute that seven hundred and sixty-three trillions enter 
the eye in a second, we experience the sensation of violet 
light. Undulations of intervening amplitudes give sensa- 
tions of other colors of the spectrum between the red and 
the violet. 

Three classes or spectra are to be distinguished. 1. 
The Continuous JSpectruin; 2. T/ie Bright-line Spec- 
trum; 3. The Dark-line Spectrum. If the light proceed 
from an incandescent solid or liquid, the spectrum is con- 
tinuous. It consists of a series of colors in their fixed 
succession, gradually shading into each other as we see 
them in the rainbow. The substance of which the incan- 
descent body is composed does not materially affect the 
spectrum. Different substances merely give variations in 
the relative widths of the different colors. 

If, however, the light proceed from an incandescent gas 
or simple substance in the state of vapor, the spectrum 
consists only of a set of bright lines. These occupy dif- 
ferent positions, and display, accordingly, different colors 
of the continuous spectrum. Now the critical fact in 
spectroscopic science is this: The bright lines produced 
by any substance are always in the same relative p>ositions 

* Solar radiations are traceable in greater wave lengths in the ultra-red, and 
in shorter wave-lengths in the ultra-violet. 



NEBULiE. 39 

in the spectrum. If we employ a different gas or vapor, 
we obtain a different set of bright, colored lines. Thus 
hydrogen gives a broad bright line in the orange, and 
narrower ones in the greenish-blue and the blue. Sodium 
vaporized gives a broad line in the yellow, which, with 
greater dispersive power of the prism-arrangements, be- 
comes a double yellow line. Light proceeding from a 
mixture of two or more gases or vapors gives the lines 
characteristic of each. One acquainted with the charac- 
teristic lines of different elements is able, on this principle, 
to indicate what substances are present in the gas or vapor 
giving a certain succession of bright lines. So constant 
are the spectroscopic cliaracters of the same substance, 
and so exact and measurable the phenomena, that our 
confidence is in no sense abated, even if we know the 
bright lines are produced by an astronomical body. 

If, finally, the light proceed from an incandescent solid 
or liquid body, and be transmitted through a gas or vapor 
at a lower temperature, we get a colored spectrum crossed 
by dark lines. And now the critical fact is this: The 
dark lines occupy the same relative positions in the spec- 
trum as the bright lines produced by the gas or vapor 
alone, lohen incandescent. In other words, the vapor or 
gas through which the light is transmitted, absorbs or 
extinguishes exactly those rays which it is capable itself 
of emitting. If the vapor alone would produce a yellow 
line, the vapor transmitting light from an incandescent 
solid or liquid produces a dark line in the place of the 
yellow. If incandescent hydrogen produce a bright line 
in the orange, an atmosphere of hydrogen transmitting 
light from a solid or liquid body will produce a dark line 
in exactly the same part of the orange.* 

*For a full exposition of the principles, methods and results of spectral 
analysis, see Schellen: Spectralanalyse, translated and republished in America 
as Spectrum Analysis in its Application to Terrestrial Substances and the Phys- 



40 COSMTCAL DUST. 

SYNOPTICAL VIEW OF SPECTROSCOPIC PRINCIPLES. 
DESIGNATION OP SPECTRUM. COXDITIOX OF MATTER. 

Continuous Spectrum [ j Incandescent Solid or Liquid 

; ( {Dnimmond Light). 

Bright-line Spectrum = 1 f^ , ^ ^^ ,„, 

Discontinuous Spectrum= ( ^ J Incandescent Gas or \ apor (^Z..- 
Direct Spectrum= I I 1 ^'^'' ^'^^^^' '^^^"^ Prominences; 

Gas Spectrum ] $[ IrresoUahh NehidcB), 

Dark-line Spectrum^ "1 " (^Incandescent Solid or Liquid 

Absorption Spectrum, ' J shining through gas or vapor 

Rever.sed* Spectrum or j | of lower temperature {Sun; 
Compound Spectrum J [ Fixed Stars). 

"When these principles are applied to the investigation 
of cosmical light, they reveal the physical conditions of 
the matter which emits it. For instance, the light of the 
moon gives the same spectrum as direct sunlight. The 
same is true of the light reflected from the planets. This, 
of course, confirms the astronomical doctrine that the 
planets and satellites shine only by reflected light. If we 
investigate the light emitted by the tail or the coma of a 
comet, we find that also to give the same spectrum as 
sun-light. Hence the tail and coma of a comet are not 
self-luminous. The nucleus of the comet, however, gives 
a spectrum of three bright lines. This demonstrates, first, 
that the nucleus is an incandescent gas or vapor; and sec- 
ondly, that it contains carbon, since the bright lines corre- 
spond to the spectrum of a compound of carbon. 

If now, we turn the spectroscope to the nebuln?, we 

ical Constitution of the Heavenly Bodies, 1872. Also in abbreviated form, 
Half -Hour Recreations in Science, Nos. 3 and 4. Boston; also Roscoe: Sf)ectrum 
Analysis, Lond., 2d ed., 1870, 8vo. pp. 404. The reader will find important and 
beautiful applications of the spectroscope in Secchi: Le Soleil, 2 vols, and 
Atlas; and Young: JTie Sun, New York, 1881. 

♦Quite commonly now, the term ''reversed" is applied to bright lines 
appearing, particular!}- in solar spectra, in the places where dark lines usually 
appear, as, for instance, in the lines due to the deepest part of the solar spots, 
and in the protuberances. See Young: The Sun, 1.30, 157, which compare with 
pages 83 and 84. See also Secchi : Le Soleil, i, 283^; ii, 83-98, etc. 



KEBUL^. ' 41 

discover that almost all those nebulae which have been 
resolved give spectra identical with the spectra of the sun 
and the ordinary fixed stars.* This is a grand consumma- 
tion. It shows that the resolvable nebulre are possibly 
what Sir William Herschel conceived them — vast firma- 
ments of suns analogous to that firmament in which our 
sun is a star. We might picture to ourselves, on the 
basis of this conception, thousands upon thousands of 
other firmaments, each with, its milky way, its constella- 
tions, its variable stars, its countless dark, unseen, but 
probably habitable planets floating away in immensity, 
each with its peculiar domestic economy, and each, never- 
theless, under the common government of a single empire 
whose ministers are gravitation, heat, light, ether. At- 
tempting to grasp the conception in its magnitude, we 
feel ourselves lifted into another realm of being. The 
limitations of earth and material existence are left be- 
hind, and we dwell, gifted with a sort of omnipresence, 
in the immensity of God's universe. 

But what of the iri^esolvahle nebulje? Their spectra 
yield only bright lines. Similar as they are in general 
aspect, to the resolvable nebulae, their spectra are funda- 
mentally different. Their physical condition, accordingly, 
is that of a glowing gas or vapor. They are not firma- 
ments of suns. They are incandescent cosmical dust. 
They are dust so intensely heated that some or all of it is 
in a state of vaporization. This is another grand consum- 
mation. A matured conjecture of Sir William Herschel 
is confirmed. The world-stuff which Laplace demanded is 
at hand. Let us see whether the aspects which it presents 
sustain the idea of progressive world-growtli. 

Evidences of development seem to be afforded by the 
forms of the nebulae. Of these we may enumerate the 
following classes : 

*It is impossible to say whether the apparently continuous spectra of some 
of these nebulie are crossed or not by darlc lines. 



42 COSMIC A L DUST. 

1. Amorphous Nebulm. — Here we may include the 
great nebula in the sword-handle of Orion.* I reproduce 
for the reader (Figure 6) the careful drawing executed by 
Trouvelot.j This is one of the brightest of the nebulae; 
but at the same time it has resisted all efforts at resolu- 
tion. Its spectrum, accordingly, consists of a small num- 




FiG. 6. The Great Nebula in Orion. Central Part. Drawn by L. 
Trouvelot. 



ber of bright lines. Here belong also, the two Magellanic 
Clouds, visible to the naked ej^e in the southern hemi- 
sphere. I am not aware that their spectrum has been 
obtained. 

2. Spiral N'ehulcB.—T\\Q nebula No. 3,239 Herschel 

* Director otto Strnve classes this among spiral nebuloe (^Monthly Notices, 
Astronomical Society, London, 14 March, 1856, xvi, 139: Gantier, Archives des 
Sciences rhysiques et Naturelles, Geneva, 186-2, translated, Smithsonian Eeport, 
1863, 299). It is possibly beginning to pass into the spiral phase. See also Prof. 
Geo. Bond : On the Spiral Structure of the great Nebula in Orion, Monthly No- 
tices, xxii, 203-7. 

t Further, on this nebula, see Nature, 22 November, 1877, p. 67, and 18 July, 
1878, p. 313; Schellen: Spectral Analysis, 534. 



NEBULA. 43 

(Figure 7) presents the form of a sickle or greatly curved 
tail of a comet. It seems to be an elongated mass of light 
just beginning a gyration about a centre a little to one 
side of the head. A remarkable spiral nebula is Herschel 
1,173.* But the most striking of all spiral nebuhie is that 
situated in Canes Venatici (H. 1,622; Figure 8). It is 




Fig 7. Sickle-shaped Nebula, IIekschel 3,239. 

impossible to gaze upon these figures without feeling 
the conviction that a spiral movement is in progress. The 
spectra of these nebulae have not been certainly ascer- 
tained ; but we may venture the conjecture that they will 
be found to consist of bright lines. Such a spectrum, at 
least, is given by the spiral nebula H. 4,0G4, in which lines 

*See view in Schellen, op. cit., 538. 



44 COSMICAL DUST. 

answering to nitrogen and hydrogen appear, besides two 
other bright lines not identified. 




Fig. 8. Spiral Nebula ix Canes Vexatici, Herschel 1.622. 

3. Spiro- annular N^ebulce. — These seem to be undergo- 
ing a transition from the spiral to the annular form. H. 604 

(Figure 9) is one of 
these. Another equal- 
ly transitional is H. 
854 (Figure 10), in 
which we see several 
segments of spiral or 
annular " forms sur- 
rounding a bright nu- 
cleus, as in H. 604. 
The spectra of these 
nebulae are also un- 

FiG.9. Spiro-axsular Nebula, Herschel 604. known.* 

* This, like most of the other nebular types mentioned may be found well 
figured in Schellen's Spectral Analysis, and better in The Popular Science 




NEBULA. 



45 




Fig. 10. Spiro-annular Nebula, Herschel 854. Indications of Several 

Rings. 

4. An7iular Nehxdm. — A fine example of this form is 
the annular nebula in the Lyre, H. 4,457 (Figure 11). Its 
spectrum consists of one bright line answering to nitrogen. 
The annular nebula is sometimes presented obliquely to 
view, as in H. 1,909. Sometimes it appears edgewise, as 
in H. 2,621. At other times it is so attenuated at oppo- 
site sides as to be invisible in those places, and appears, 
accordingly, as a double nebula, as in H. 3,501 and H. 
2,552. More powerful instruments may be expected to 
show the ring complete. In both these cases there is a 
central mass more or less luminous, as in H. 854, H. 604 
and H. 4,447. The nebula. Figure 10, seems likely to 



Monthly for June, 1873. Newcomb's Popular Astronomy also gives views of 
The Great Nebula in Orion, the Annular Nebula in the Lyre, the Omega Nebula 
H. 2,008, the Nebula H. 3,722, and the Looped Nebula H. 2,941. But the most 
exquisitely delicate representations of nebulae are found on two plates of Secchi: 
Le Soleil, vol. ii. . 



46 



COSMICAL DUST. 




Fig. 11. Annular Nebula in the Ltre 
From a Drawing by Prof. Holden. 



consist of a central mass 
surrounded by several 
rings which may be 
hereafter more distinct- 
ly discerned. 

5. Planetary N'ehulm, 
— These are nebulas with 
tolerably definite circu- 
lar outlines, and consist 
either of a uniform disc, 
as defined by Herschel, 
or of a rudely annular 
or spiral belt surround- 
ing a faint luminosity, 
which often contains one 
or more bright nuclei. 
The bright belt is often fringed by a coma or a bur of 
light. H. 2,241, as shown in Figure 12, consists of a well 
defined- belt of light surrounded 
by an irregular coma, but without 
a nucleus. H. 464 shows a bright 
ring of the spiral order. It is 
surrounded by a bur of light, 
and has two nuclei which scarce- 
ly sustain any relations to the 
general structure. H. 838, Fig- 
ure 13, has a ring of light consist- 
ing of a double bami of the spiral 
order. It is surrounded by a bur 
of light, and contains two nuclei 
symmetrically situated, and surrounded each by a dark 
zone, a luminous haze and a bright ring. The planetary 
nebula in Aquarius (H. 2,098), consists of a sphere of 
luminosity surrounded by a fringe of rays. From each 
side of the sphere projects a protuberance equal in length 




Fig. 12. 

Planetary Nebula, H. 2,-i41 

Without a Nucleus. 



NEBUL.^. 



47 




Fig. 13. 
Planetary Nebula, H. 
WITH TWO Nuclei. 



to the radius of the sphere. 
Tliis phenomenon, it has 
been suggested, may result 
from edgewise presentation 
of a ring. This nebula gives 
a spectrum of three bright 
lines, one of which is due to 
hydrogen and one to nitro- 
gen. 

G. Stellar Nehulce.—ThQue 
consist of a bright nucleus 
more or less resembling a 
star, which is surrounded by 
a disc of light, sometimes in alternating bands of bright- 
ness. The nebula H. 450 is one of this class, very strongly 
marked, and it has a spectrum of three bright lines. One 
cannot help remarking the resemblance to a stellar nebula 
presented by Donati's comet, on the second of June, 1858. 
When the central body is sharply defined like a star, the 
object is known as a "nebulous star." 

The six foregoing classes of nebulae all give, so far as 
ascertained, spectra of bright lines. They are, therefore, 
masses of glowing gas. About sixty nebulae have been 
investigated by Huggins spectroscopically, with results 
which are satisfactory for the present. A much larger 
number were found too faint to yield results which could 
be relied upon. Of the sixty, about one-third yield 
spectra of bright lines, and about two-thirds yield spectra 
apparently continuous. It is an interesting fact that all 
nebulae giving bright-line spectra remain completely irre- 
solvable; and all nebulae which are resolvable give continu- 
ous spectra. The "resolvable nebulas," therefore, do not 
constitute a class of proper nebulae. More than Imlf of 
those forms once regarded as nebula3 must be set down as 



48 COSMICAL DUST. 

starry clusters.* But at least one-third of all so-called 
nebulae are real nebulae — masses of incandescent vapor. 

§ 6. UNIVERSAL WORLD-STUFF. 

1. Cosmical Dust. — The cosmical realm appears, from 
the survey which we have taken, to be abundantly stocked 
with the crude material of which worlds are formed. The 
most familiar substances of our earth are found in meteor- 
ites, comets, and irresolvable nebulae, as well as in resolv- 
able nebulae, stars and suns. But one system of matter 
pervades the immense spaces of the visible universe; and 
it is a dream of physical philosophy that all the recognized 
chemical elements will one day be found but modifications 
of a single material element.f When this dream is real- 

* Prof. Newcomb, Popular Astronomy, p. 444, has given views of two such 
"clusters." 

+ It is generally admitted that at excessively high temperatures, matter 
exists in a state of dissociation— that is, no chemical combination can exist. 
Now, if the so-called elements are really compounded, a state of dissociation 
would resolve them into ultimate atoms or molecules, all of one kind. The 
spectrum of such a substance should be a bright line. If the temperature is 
such that two or three different molecular arrangements may exist, the spectrum 
should consist of two or three bright lines. The question may reasonably be 
raised whether the nebulae which give two or three bright lines are in such a 
condition. Dumas, in 1857, based the suggestion of the composite nature of the 
'■ elements " on certain relations of atomic weights. (See also Comptes Eendus, 
Nov. 3, 18T3.) The conception was maintiiined in 1866, and subsequently, by 
Professor G. Hinrichs {Atomechanik; also Amer. Jour. Sci., II, xxx, ]9, 56, id. 
Ill, i, 319), from a consideration of the physical properties of the atoms; and 
further, in 1874, from the relations of atomicity and atomic weights (G. Hin- 
richs: The Principles of Chemistry and Molecular Mechanics, 182. See also, 
Affier. Jour. Sci., II, xxxii, 350, and Proc. Amer. J.«S(9C., 1869, 112). Berthelot 
maintains that the atoms of the elements are composed of the same matter, dis- 
tinguished only by the motions set up in them; and accordingly H. Ste. Claire 
Deville affirms that " when bodies deemed to be simple combine with one 
another, they vanish, they are individually annihilated." Dr. E. Haanel has 
clearly shown that the phenomena of allotropism and combining proportions 
demand the admission of the complex constitution of the elements (address 
before the Ontario Association for the Advancement of Education, 1876). Pro- 
fessor Lockyer has published some strikingly confirmatory conclusions based on 
spectroscopic phenomena (J. N. Lockyer: Discussion of the Working Hypoth- 
esis that the So-called Elements are Compound Bodies, Proc. Boy. Soc, xxviii, 
159, 12 Dec, 1878; Comptes Bendus^ Nov., 1878; Amer. Jour. /Sd., Ill, xvu, 64, 



WORLD-STUFF. 49 

ized, we shall behold the amazing phenomenon of a 
universe with its numberless forms, conditions and aspects 
built out of a single substance. 

2. Elemental Atoms. — The conception of matter of 
some sort existing in a highly attenuated state throughout 
the remote regions of space appears to be as old as the 
age of Newton. Indeed, the doctrine of the universal 
diffusion of material stuff in a chaotic period, before the 
organization of the universe, was a central conception of 
the Greek atomists, as well as of all those physical specu- 
lators who maintained the theory of a plenum, down to 
Descartes.* The doctrine of attenuated matter diffused 
through the intercosmical spaces of organized systems is 
distinct. Dr. T. S. Hunt has called attentionj to some 

93-116; Nature, xxi, 5; xxii, 4-7, xxiv, 396, Aug. 25, 1881. Necessity for a New 
Departure in Spectrum Analysis {Nature, Nov. 6, 1879, Oompies Rendus, xcii, 904) . 
But see criticisms on Lockyer's views by H. W. Vogel, Monatsher. der Berliner 
Akad. der Wiss., 1880, 192 and Nov. 2, 1882, Nature, xxvii, 233; also by Liveing 
and Dewar, Proc. Roy. Soc, 30, 93 ; V/ied. Beibl. iv, 366. See also results attained 
by A. Schuster, Nature, xxii, 444, Prof. F. W. Clarke entertains kindred views 
{Pop. Set. Monthly, ii, 32, Jan. 1873; Science News, Feb. 15, 1879, 114). Dr. J. G. 
Macvicar has also speculated on the assumed identity of the ultimate elements, 
and their common constitution with the ethereal fluid (A Sketch of a Philosophy, 
Parts I and II, London, 1868); while the late remarkable experiments of Dr. 
Crooks on so-called " radiant matter'' (W. C, Crooks, Nature, xxii, 101-4, 125-8, 
\^?,-\, Amer. Jour. Sci.lll, xvii, 281 ; xviii, 241-62; Pop. Science Monthly, x.\'\, 
13-24, 157-67), would seem to be best understood on the hypothesis of the homo- 
geneity of the elements of matter, and the continuity of the states of matter. 
The ethereal ground of all matter is also maintained by M. Moigno {Acad, des 
Sci., April 16, 1883, and by Prof. Oliver Lodge {Nature, xxvii, 304-6, 328-30. par- 
ticularly p. 330), whose position is criticised by S. Tolver Preston {Nature, xxvii, 
579). See also Newton's suggestions given below. The final demonstration 
seems, therefore, to be impending, and the dream of science is promised a 
fulfilment. See further on this subject the suggestive lecture of Sir Benjamin 
Brodie on Ideal Chemistry, 1867, reprinted 1H80, as also a very accessible paper 
by Professor F, W. Clarke in Popular Science Monthly, No. xlvi, Feb. 1876, 
463-71; but more i)articular]y in reference to the cosmical diffusion of disso- 
ciated matter, see beyond with the appended references. 

* See Part iv of this work. 

t Hunt : Celestial Che?nistry from the Time of Newton, read before the 
Cambridge Philosophical Society, Nov. 28, 1881, reprinted from its Proceedings, 
Amer. Jour. Sci. IIL xxiii, 123-33, Feb., 1882. I have depended greatly on Dr 
Hunt's suggestions in arranging the historical memoranda which follow. 

4 



50 COSMIOAL DUST. 

long-neglected passages in Newton's works, from which it 
appears that a belief in such universal, intercosmical 
medium gradually took root- in his mind. Newton, as his 
well known letter to Bentley proves, was persuaded that 
the power of attraction could not be exerted by matter 
across a vacuum. These passages show what were his 
views respecting the nature of the interplanetary medium 
of communication. Though declarino^ that *'the heavens 
are void of all sensible matter," he elsewhere excepted 
"perhaps some very thin vapors, steams and effluvia, aris- 
ing from the atmospheres of the earth, planets and comets, 
and from such an exceedingly rare ethereal medium as we 
have elsewhere described."* The "ethereal medium" 
referred to here had been suggested in his "Hj'pothesis," 
of 1675, where he imagines "an ethereal medium much of 
the same constitution with air, but far rarer, subtler and 
more elastic." "But it is not to be supposed that this 
medium is one uniform matter, but composed partly of 
the main phlegmatic body of ether, partly of other various 
ethereal spirits, much after the manner that air is com- 
pounded of the phlegmatic body of air intermixed with 
various vapors and exhalations." He conceives this me- 
dium to be in continual movement and' interchange. " For 
nature is a perpetual circulatory worker, generating fluids 
out of solids, fixed things out of volatile, and volatile out 
of fixed; subtile out of gross, and gross out of subtile; 
some things to ascend and make the upper terrestrial 
juices, rivers and the atmosphere, and by consequence, 
others to descend for a requital to the former. And as 
the earth, so perhaps may the sun imbibe this spirit copi- 
ously to conserve his shining and keep the planets from 
receding further from him; and they that will may also 
suppose that this spirit affords or carries with it thither 

* Newton: Optics, Bk. Ill, Query 28, 1704. 



WOKLD-STUFF. 51 

the solary fuel and material principle of life, and that the 
vast ethereal spaces between us and the stars are for a 
sufficient repository for this food of the sun and planets." 
Then rising to a still higher generalization, he adds: 
" Perhaps the whole frame of nature may be nothing but 
various contextures of some certain ethereal spirits or 
vapors, condensed, as it were, by precipitation, much after 
the same manner that vapors are condensed into water or 
exhalations into grosser substances, though not so easily 
condensable, and after condensation wrought into various 
forms; at first by the immediate hand of the Creator, and 
ever since by the power of nature, which, by virtue of the 
command 'increase and multiply,' became a complete imi- 
tator of the copy set her by the great Protoplast. Thus, 
perhaps, may all things be originated from ether." 

Twelve years later* Newton strengthened this hypothe- 
sis by additional considerations. The tails of comets 
were conceived to afford exhalations which, with progres- 
sive rarefaction and dilatation, spread throughout space, 
and being thus brought under the attraction of the planets, 
mingle with their atmospheres and contribute support 
for vegetable life. But since vegetation when decaying 
passes in part into solid states, while fluids are demanded 
for the continued sustenance of the vegetable kingdom, 
the continued supply of these fluids must come from some 
external source. This supply, he thought, might originate 
chiefly in the tails of comets. 

Still later f he conceived that similar exhalations might 
proceed from other celestial bodies, for he speaks of the 
sun and fixed stars as great earths, intensely heated and 
surrounded with dense atmospheres which, by their weight, 
condense the exhalations arising from these hot bodies. 
In succeeding editions he develops the idea of exhalations 

* Principia, Bk. Ill, prop. 41, 1st. ed. 1687. 
t Newton: Optics, 1st. ed., 1704, Query 11, 



52 COSMICAL DUST. 

or vapors proceeding from the sun and other heavenly 
bodies, and by expansion "through all the heavens," con- 
stituting a medium universally diffused. This theory con- 
tinued to take more definite shape in the mind of Newton 
till, in the latest editions of the Principia and Optics, 
he enunciates the clear conception of a thin interstellary 
matter "arising from the sun, the fixed stars and the tails 
of comets, and falling by gravity into the atmospheres of 
the planets, there becoming condensed and passing gradu- 
ally, through the influence of gentle heat, into the form 
of salts, sulphurs (that is, combustible matters), tinc- 
tures, slime, mud, clay, sandstones, coral and other terres- 
trial substances."* 

The notion of the existence of a subtile ethereal medium, 
suggested, as is thought, by passages in the works of Sir 
Isaac Newton, maintained a place in scientific and philo- 
sophic speculations,! but the somewhat different notion 
of a diffused matter not dift'ering in its substance from 
ordinary matter, met with almost no response until 1842, 
when Professor W. R. Grove, in a lecture at the London 
Institution, propounded the theory that heat and light are 
affections "of matter itself, and not of a distinct ethereal 
fluid permeating it; " and he added: "With regard to the 
planetary spaces, the diminishing periods of comets is a 
strong argument for the existence of a universally dif- 
fused matter; this has the function of resistance, and 
there appears to be no reason to divest it of i\\e functions 
common to all matter.'^^\ In his essay on the Correlation 
of the Physical Forces, published in 1843, he suggested 

* Newton: Principia, lib. Ill, prop. xlii. 

t See especially Comte: Philof^opliie PosUive; Helmholtz: Interaction of 
the Natural Forces; Sir William Thomson : Density of the Luminrferous Ether, 
Trans. Eoy. Soc. Edinb., xxi, Pt. i, 1854, Phil. Mag. ix, 36, 1855. 

% Grovo: Correlation of the Physical Forces, Youmans" ed.. Preface, 6 and 
T, The anthor subsequently states (p. 12;^) that "the celebrated Leonard Enler 
had published a somewhat similar theory.'" 



WORLD-STUFF. 53 

that "worlds or systems" "are gradually changing by 
atmospheric additions or subtractions, or by accretions or 
diminutions arising from nebulous substance, or from 
meteoric bodies'''' (p. 81). His whole essay is grounded on 
the general doctrine that the so-called "imponderable" 
agents are nothing but "modes of motion" in ordinary 
matter excessively attenuated and universally diffused.* 
In a later edition he suggests that the planetary and 
stellar atmospheres, expanded through space, are probably 
in " a state of equilibriiun with reference to each other," 
and may "furnish matter for the transmission of the 
modes of motion, which we call light, heat," etc. In 1866 
he still further suggested f that this diffused matter may 
become a source of solar heat, "inasmuch as th'e sun may 
condense gaseous matter as it travels in space, and so heat 
may be produced.' 

Almost simultaneously with Grove, Humboldt J placed 
on record his belief that "exact and corresponding obser- 
vations indicate the existence and the general distribution 
of an apparently non-luminous, infinitely divided matter." 
* * * "Of this impending ethereal and cosmical matter 
it may be supposed that it is in motion / that it gravi- 
tates, notwithstanding its original tenuity; that it is con- 
densed in the vicinity of the great mass of the sun; and 
finally, that it may, for myriads of ages, have been aug- 
mented by the vapor emanating from the tails of comets." 
It is not clear from Humboldt's language that he enter- 
tained a conception of diffused common matter, or only of 
a peculiar fluid, like that insisted on by Dr. Young. What 
he says is in connection with the assumed ethereal resist- 

*See, for instance, pp. 81, 123, 138, 139, 151, 187, 198. 

t Address as President of the British Association, 1866. 

i Humboldt: Kosmos, Otte translation. Harpers" ed., i, 86. Tlie autlior tells 
us in his preface that the work was written for the first time in the years 1843 
and 1844, though he had "for many months'' previously delivered lectures on 
the themes embraced, in Paris and Berlin. 



54 COSMICAL DUST. 

ance to the motion of Encke's comet; and, in another pas- 
sage, speaking of "the vaporous matter of the immeasur- 
able regions of space," he adds, " whether scattered with- 
out definite form and limits, it exists as a cosmical ether, 
or is condensed into nebulous spots." His interchanges of 
terms, however, are similar to those employed by Newton, 
and it is probable that Humboldt did not imagine any 
*' cosmical ether" having an essential constitution differ- 
ent from that of ordinary matter. 

Sir William Thompson in 185-i,* in a note on the pos- 
sible density of the luminiferous ether, expresses the opin- 
ion that this substance is " most probably a continuation 
of our own atmosphere." Sir Benjamin Brodie, on the 
3d of May, 1866, f read a memoir in which he advanced 
the idea that many ultimate chemical elements now only 
known in combination "may sometimes become, or may in 
the past have been, isolated and independent existences,'''' 
and on the 6th of June of the following year he pursued 
the thought further,^ advancing the suggestion that " in 
remote ages, the temperature of matter was much higher 
than it is now, and that these other things (the ideal ele- 
ments) existed in a state of perfect gas — separate exist- 
ences — un combined." 

But quite independently, and a few days earlier than Dr. 
Brodie's last mentioned utterance, very similar views were 
set forth by Dr. T. S. Hunt. In a lecture on the Chemistry 
of the Primeval Earth, % he advanced the opinion that the 
"breaking up of compounds, or dissociatioitof elements, by 
intense heat, is a principle of universal application, so that 

* Thomson, Trans. Boy. Soc. Edinb., xxi, pt. i: Phil. Mag., ix, 36, 1855. 

+ Brodie: Calculus of Chemical Operations, Proc. Roj-al Soc, May 3, 1866, 
Phil. Trans., 186G. 

:;: Brodie: Ideal Chemistry, a lecture before the Chemical Society of London, 
Jane 6, 1867, published in the Chemical News, June 14, 1867: republished 1880, 
in separate form, with a preface. 

§ Delivered before the Royal Institution, May .31, 1867, and published in the 
Chemical yews of June 21, 1867, and in the Proceedings of the Royal Institution. 



WORLD-STUFF. 55 

we may suppose that all the elements which make up the 
sun, or our planet, would when so intensely heated as to 
be in the gaseous condition which all matter is capable 
of assuming, remain uncombined; that is to say, would 
exist together in the state of chemical elements; whose fur- 
ther dissociation in stellar or nebulous masses may even 
give us evidence of matter still more elemental than that 
revealed in the experiments of the laboratory, where we 
can only conjecture the compound nature of many of the 
so-called elementary substances." Seven years later. 
Dr. Hunt * repeated the expression of these views, and 
added the hypothesis suggested by Sir William Thomson, 
that our atmosphere and ocean are but portions of the uni- 
versal medium which, in an attenuated form, fills the 
interstellary spaces; and added further, that "these same 
nebulae and their resulting worlds may be evolved by a pro- 
cess of chemical condensation from the universal atmos- 
phere, to which they would sustain a relation somewhat 
analogous to that of clouds and rain to the aqueous 
vapor around us."t 

Similar views, in apparent unconsciousness of their 
suggestion by preceding writers, were put forth in 1870, 
by Mr. W. Mattieu Williams,^ who conceived, as Grove 
had done in 1866, that the sun's heat is maintained by his 
condensation of attenuated matter everywhere encoun- 

*In an address at the grave of Priestley, on A Centunfs Progress in Theo- 
retical Chemistnj, delivered at Northumberland, Pa., July 31, 1874; American 
Chemist, v, 46-61 ; Pop. Sci. Monthly, vi, 420. 

t See these views reiterated in Preface to his second edition of Chemical and 
Geological Essays, 1878, pp. ix-xix; again at meeting of British Assoc, Dublin, 
reported in Nature, xviii, 475, Aug. 29, 1878; and also before the French Acad- 
emy of Sciences, published in Comptes Rendus, Ixxxvii, 452, Sep. 23, 1878; and 
still further developed in an essay on the Chemical and Geological Relations of 
the Atmosphere, Amer. Jour. Sci., Ill, xix, 349-63, May, 1880; and finally, in a 
communication in Nature, xxv, 602-3, Apr. 27, 1882. 

i: Williams: The Fuel of the Sun. A condensed statement of the contents 
of this work is contained in Current Discussions in Science by the same author 
in "Humboldt Library,'" No. 41, Feb. 1883. See, also, Williams on the Radi- 
ometer and its Lessons, Quar. Jour. Science, Oct. 1876. 



56 COSMICAL DUST. 

tered in his motion through interstellary space. This 
matter is essentially the attenuated state of the atmos- 
phere surrounding the cosmical bodies. He suggested 
that this diffused matter or ether which is the recipient 
of the heat radiations of the universe, is thereby drawn 
into the depths of the solar mass. Expelling thence the 
previously condensed and thermally exhausted ether, it 
becomes compressed and gives up its heat, to be in turn 
itself driven out in a rarefied and cooled state, and to absorb 
a fresh supply of heat which he supposes to be in this 
way taken up by the ether, and again concentrated and 
redistributed by the suns of the universe (chapter Y). 

Mr. Williams' suggestion was adopted by Dr. P. Mar- 
tin Duncan * who, in 18T7, also without the knowledge of 
Grove's priority, but also rejecting Williams' assumption 
of the equilibrated condition of the atmospheres of the 
heavenly bodies, conceived the sun to be slowly attracting 
to itself the earth's atmospheric envelope, and proceeds to 
deduce from this premise a secular diminution of the 
earth's climatic warmth. f 

There are few investigations the history of which better 
illustrates the interesting coincidences of conviction in 
different minds working in complete personal indepen- 
dence of each other. Some recently propounded theory or 
conjecture, or some scientific stadium reached through the 
combined efforts of many investigators, seems to set 
many intellects in a similar mood, in which, by the laws 
of thought, expectation and attention are turned in one 
common direction, so that some new conception springs 
into existence independently in many minds. This princi- 
ple is still further exemplified in connection with the doc- 

*In an address as President of the Geological Society, London, May, 1877. 

tThe cosmical bearing of the doctrine of dissociation of matter at high 
temperatures is also implied in the publications of Prof. F. W. Clarke and Mr. 
Lockyer. previously cited. 



WORLD-STUFF. 6*^ 

trine of disseminated matter in the case of a recent theory 
wliich it remains to present. Dr. C. William Siemens in a 
recent memoir of extraordinary interest, 0)i the Conserva- 
tion of Solar Energy,"^ catching hold of the suggestions 
of his predecessors respecting an all-pervading medium, 
has followed Grove in seeking through its condensation 
the source of solar heat, though summoning to his aid 
a mechanism both original and striking. He supposes 
stellar space "to be filled with highly rarefied gaseous 
bodies, including hydrogen, oxygen, nitrogen, carbon and 
their compounds, besides solid materials in the form of 
dust. This being the case, each planetary body would 
attract to itself an atmosphere depending for its density 
upon its relative attractive importance, and it would not 
seem unreasonable to suppose that the heavier and less 
diffusible gases w^ould form the staple of these atmos- 
pheres, that in fact, they would consist mostly of nitro- 
gen, oxygen and carbonic anhydride, whilst hydrogen and 
its compounds would predominate in space. f But the 
planetary system as a whole would exercise an attractive 
influence upon the gaseous matter diffused through space, 
and would therefore be surrounded by an interplanetary 

* Read at the Royal Society, London, March 2, 1882, and first published in 
Nature^ xxv, 440-4, March 9, 1882, See a criticism by E. Douglass Archibald, 
and Dr. Siemens' reply, in Nature, xxv, 504. See also supplementary views by 
Charles Morris of Philadelphia and Dr. T. S. Hunt of Montreal, together with 
Dr. Siemens' response, in Nature^ xxv, 601-3, April 27, 1882; also Prof. S. D. 
Liveings notice in address as President of the Chemical Section, British 
Association, Nature xxvi, 404-5, August 24, 1882. This memoir was also pub- 
lished, with some modifications and additions, in The Nineteenth Century, May 
1883. The Pojudar Science Monthly, June, 1882, in Annates de Chimie et de 
Physique, and other journals. 

t On this theory an atmosphere ought to be collected about the moon, of 
one-sixth the density of the terrestrial atmosphere. That is, the moon should 
possess an atmosphere capable of producing some discernible refraction. Also 
Jupiter should possess an atmosphere more conspicuous than that of Mars, in 
proportion as his effective surface attraction is greater. Dr. T. S. Hunt re- 
minds us that according to Saemann the moon's atmosphere has been absorbed; 
but then we have to inquire what has prevented renewed condensation about 
the moon?— even after all pores of the moon have been filled. 



68 COSMICAL DUST 

atmosphere holding an intermediate position between the 
planetary atmospheres and the extremely rarefied stellar 
space," 

This conception is supported by the consequences of 
the molecular theory of gases as laid down by Clerk Max- 
well, Clausius and Thomson; since it would be difficult to 
assign a limit to a gaseous atmosphere in space. Further, 
it has been directly asserted by various authors from New- 
ton down, as I have already shown; and Dr. Flight, like 
others before him, has detected in meteoric stones large 
quantities of occluded carbonic oxyde, hydrogen and ni- 
trogen, with smaller amounts of light carburetted hydrogen 
or marsh gas, and carbonic anhydride ; * all which gases 
must have been absorbed in distant space, as the time of 
flight through our atmosphere is too brief, and the heat 
produced by friction too great. Again, spectrum analysis 
indicates the presence of gaseous matter in space; and 
according to the testimony of Dr. Huggins, carbon, hydro- 
gen, nitrogen and probably ox3'gen exist in cometary 
nuclei, while, according to the views of Dewar and Live- 
ing, nitrogenous compounds, such as cyanogen, are also 
present. Dr. Siemens thinks aqueous vapor present in 
space, though it is not detected in meteoric stones in con- 
sequence of the intense heat to which they have been sub- 
jected. Captain Abney found benzine and ethyl in the 
atmosphere at sea-level, and in equal quantities at the 
altitude of 8,500 feet.f 

Applying these conceptions to the problem of solar 
heat. Dr. Siemens holds that the sun and planets commu- 
nicate some of their own motion of rotation to the atmos- 
pheres condensed about them, and he supposes that in this 

*The folic. ving are the proportions: CO-2, 0.12; CO, 31.88; H, 45.79; CH4, 
4.55; N, 17.66: Total, 100. Some meteoric stones have been found to contain 
six times their own volume of these gases. 

t Nature, xxvi, 586. 



WORLD-STUFF. 59 

way an action like that of a blowing fan is set up, by 
which the equatorial part of the sun's atmosphere acquires 
such a velocity as to stream out to a distance beyond the 
earth's orbit, while an equal quantity of gas is drawn in 
at the poles to maintain equilibrium. The gases thus 
driven to a distance in planetary space must, of course, 
be enormously expanded and highly attenuated, and in 
this state Dr. Siemens thinks that such of them as are 
compound may be decomposed by absorbing the solar 
radiation, and thus the kinetic energy of solar radiation 
be converted into the potential energy of chemical separa- 
tion. These dissociated vapors, in consequence of the fan- 
like action resulting from the rotation of the sun, must 
eventually be drawn in again at the polar regions. Here, 
becoming heated both by increased density and by solar 
emission, they would burst into flame at a point where 
both their density and temperature should have reached 
the necessary elevation to induce combustion. The re- 
sulting aqueous vapor, carbonic anhydride and carbonic 
oxide would be drawn toward the equatorial regions, and 
be there again projected into space by centrifugal force.* 
The annexed diagram, accompanying Dr. Siemens' 
memoir, is described by him as " an ideal corona repre- 
senting an accumulation of igneous matter upon the solar 
surfaces, surrounded by disturbed regions pierced by occa- 
sional vortices and outbursts of metallic vapors, and cul- 
minating in outward streams projecting from the equatorial 
surfaces into space through many thousands of miles." 
Dr. Siemens states that an American observer has informed 

*The conditions, it will be perceived, are not those of a rotating body sur- 
rounded by empty space. In the latter case, the centrifugal force of the sun 
would need to be increased eighteen thousand times, by a rotary velocity one 
hundred and thirty -four times as great. But on the postulate of this theory, that 
all space is filled with similar matter, the gaseous products here considered 
would be in a state of equilibrium, floating like particles in an atmosphere, so that 
any amount of centrifugal force would suffice to project them away from the ro- 
tating body. 



60 



COSMiCAL DUST. 




Fig. 



14. Ideal iLLusTUATfON of the Streams of Outflow ing and 
Inflowing Matter upon the Sun. After Siemens. 



WORLD-STUFF. 61 

him that this diagram " bears a very close resemblance to 
the corona observed in America on tlic occasion of the 
total eclipse of the sun on the 11th of January, 1880. 

In later communications, Dr. Siemens has suggested 
other confirmations of his view, specifying the zodiacal 
light and the spectroscopic researches of Captain Abney, 
communicated to the British Association in August, 1882, 
demonstrating the existence of carbon compounds proba- 
bly analogous to ethyl, and at a low temperature, between 
the atmosphere of the sun and that of the earth. He 
refers also to the experiments made by S. P. Langley 
(with the bolometer), the observations of Professor 
Schwedoff (yet unpublished), as well as the older obser- 
vations of R. G. Carrington on the movements of sun- 
spots.* 

Thus, so far, the phenomenon of solar heat is simply 
one term in the cycle of expansion, dissociation, condensa- 
tion and recombination, indefinitely repeated. But such a 
process, even if real, cannot perpetuate solar heat through 
eternity. It simply delays final refrigeration; since the 
actual enormous radiation of the sun remains the same, 
and diminishes daily by a positive amount the aggregate 
of solar energy to be employed in reproducing solar heat.f 

We ought not perhaps, to dismiss Dr. Siemens' theory 
without stating some physical difficulties which have been 
charged against it. The following may be mentioned: 

(1.) It icoald introduce a disturhing mass of matter 
within the solar si/stem.l The attenuated matter which 
the theory supposes, would be attracted to the sun and 

* Siemens, Compfes Rendus, xcv, 771, 1012, Oct. 30 and Nov. 27, 1882. 

tFor a thoughtful paper touching the general subject of " Matter in Space," 
see Charles Morris (Philadelphia!, in Nature, xxvii, SIO-.ol, Feb. 8, 1883. In con- 
tinuation of the same line of thought, see a paper by A. S. Ilerschel in Nature, 
xxvii, 458, 504-6. 

X M. Faye, Comptes Rendus, Oct. 9, 1882, p. 612; also Hirn, Comptes Rendus, 
^o\. 6, 1882, p. 812-4. 



62 COSMICAL DUST. 

stars, as M. Faye maintains, and would increase their mass. 
It would also constitute, disseminated through space, an 
important hindrance to the motions of the heavenly 
bodies. A litre of air containing the requisite amount of 
aqueous vapor weighs at least one gram at ordinary pres- 
sure. At a pressure of g-oVo"? which is assumed by Dr. 
Siemens, this will amount to 0.0005 gram, and a cubic 
metre will weigh 0.005 kilogram. If we consider the solar 
system as a sphere which will include the planets as far as 
Neptune, the weight of the extremely rarefied matter 
added to the solar system would be 100,000 times the 
weight of the sun.* Such an addition is phj^sically inad- 
missible. 

The first part of this objection is manifestly disposed 
of by the state of spatial equilibrium assumed by Dr. 
Siemens, and which is the express condition of the equa- 
torial outflow, since this is a condition which would pre- 
vent the gravitation of the matter toward the sun and 
stars in any other sense than a possible diminution of 
tenuity in their neighborhood. This part of the objection 
does not apply to matter in a state of circulation about 
centres of attraction.! 

The influence of such assumed vapors or gases as a 
resisting medium upon the motions of the heavenly 
bodies, has been more especially insisted upon by M. 

*The matter added would be, in kilograms, |rr (6400000 X 24000 X 30 )» X 
0.0005 kilog. ; where the first factor in the parenthesis is the earth's radius in 
metres, the second is the number of earth-radii in the earth's distance from the 
sur, and the third is the number of times Neptune's distance from the sun ex- 
ceeds the earth's. The weight of the sun, similarly, would be |7r, 64030000)' 
X 5.6 X 3-24000 kilog. ; where the first number is the radius of the earth in deci- 
metres, the second the mean densitj- of the earth, and the third the sun's mass 
relative to the earth. The first of these expressions is 100,000 times as great as 
the second, and would imply that there exists in the solar system nearly 100,000 
times as much matter as has been recognized in the delicate calculations of 
celestial mechanics. 

tDr. Siemens, in replying to M. Faj^e's objections, holds that the density of 
the matter may probably be reduced to one-millionth of one atmosphere. 
Comptes SenduSy 30 Oct. 1882, p. 771. 



WORLD-STUFF. 63 

Hirn.* Referring to Laplace's determination that the 
total retardation of the earth in its orbit in three thousand 
years cannot exceed ninety seconds, he states that such 
retardation would be caused by a gaseous medium of such 
tenuity that one kilogram should occupy seven hundred 
billion cubic metres of space, and that even one ten-quad- 
rillionth of a kilogram in a cubic metre (one kilogram in 
ten quadrillion cubic metres) would suffice to sweep the 
earth's atmosphere away in a few minutes. To this Dr. 
Siemens replies by referring to Froude's experiments 
which seem to show that a solid moving through a perfect 
fluid would experience no resistance ;t and to the experi- 
ments of Messrs. Fowler and Walker which demonstrate 
that the pressure of wind against surfaces is not propor- 
proportional to their area; from which it is inferred that 
a planet may move through a rare and highly fluid 
medium with very little resistance. Moreover, according 
to the third law of Kepler, a diminution of tangential 
velocity should lead to a diminution of distance from the 
centre of attraction, and thus an acceleration of an angular 
velocity which would neutralize the retardation. 

This discussion, it will be noticed, does not particularly 
concern the existence of small masses and particles some- 
what widely scattered in space. 

(2.) The atomic dissociations and associations would 
neutralize each other. X Granting that the compounds 
dissociated in space, as Dr. Siemens assumes, by solar 
and stellar radiations, become recombined on approaching 
the sun, the recombinations would become dissolved again 
on attaining the full temperature of the sun's surface, as 
the sun's heat is believed to hold in a state of dissociation 
the matters which enter into his constitution. Thus, the 

*Hirn, Comptes Bendus, xcv, 813-4. 

+ Siemens, Comptes Bendus, xcv, 1040. 

t M. G. A. Hirn, Comptes Bendus, Nov. 6, 1883. 



64 COSMICAL DUST. 

heat given out by recombination would be lost by the final 
decomposition, and the sun would gain nothing. 

This is undoubtedly true if the dissociation effected in 
immediate contact with the sun is as complete as that 
effected in the interstellar spaces. Dr. Siemens, in reply- 
ing to M. Hirn's objections,* maintains that such is not 
the fact, since the sun's photosphere cannot be admitted 
to possess a temperature above 3000° C. It may be fur- 
ther suggested that dissociation in the sun's photosphere 
is by no one sup230sed to proceed further than the dis- 
engagement of the elements known to chemistry, while 
recent science, as I have shown (p. 48), renders probable 
an ultimate atomic dissolution in other regions of space. 

(3.) The employ ment of stellar radiations in effecting 
interstellar dissociation xcoidd imply a more rapid dim- 
inution of the intensity of light than the laic of inverse 
squares of the distances p)ermits.\ The inherent luminos- 
ity of the heavenly bodies must therefore be greater than 
it appears; but there exists no independent ground for 
supposing the intensity of light varies materially from the 
law of inverse squares. 

If this conclusion is admitted, it seems to furnish no 
evidence against the theory. Professor S. P. Langley % 
has shown that a large part of the solar radiations is 
absorbed by the sun's atmosphere, and another part by the 
earth's. Indeed it has long been known that the sensible 
solar intensity is not in accordance with the law of inverse 
squares of the distances. Moreover, the late experiments 
of Captain x\bney indicate, on independent grounds, the 
existence of an interplanetary fluid of such nature as tlie 
Siemens theory requires. And lasth% M. Janssen has an- 
nounced as one of the results of his observation of the 



* Siemens, Comptes Rendus, xcv, 1037-43. 

tM. G. A. Him, Comptes Eendus, Nov, 6, 1882, pp. 812-4. 

4: See especially an important paper in Ame?'. Jour. Sci., III. xxv. 169-96. 



A THEORY. 65 

solar eclipse of May, 1883, the "discovery of the Frauen- 
hofer spectrum and the dark lines of the solar spectrum 
in the corona, showing cosmical matter around the sun." * 

Finally, so far as Dr. Siemens' theory of the reproduc- 
tion of solar heat has any substantial basis, the doctrine 
of the spatial dissemination of ordinary matter in its ele- 
mental or atomic state receives confirmation. 

We may now present a conspectus of the principal con- 
ceptions entertained respecting the contents of the inter- 
cosmical spaces: 

Intercosmical space a vacuum _ _ - Laplace, etc. 

Iiitercosmical space a plenum (Des Cartes, etc.). 
Filled with a peculiar ethereal fluid. 

Common matter not generally diffused - Young, etc. 
Common matter existing as cosmical dust Nordenskjold. 
Filled only with common matter excessively 
attenuated. 

i EuLER, Grove, 
Meteoroidal masses not specially important -j Humboldt, Hunt, 

( Siemens. 
Meteoroidal masses performing an impor- 
tant part. - - - - - Tms WORK. 

§ 7. A COSMICAL SPECULATION. 

Hypothesis is the life-hlood of investigation.— Lockyer. 

Nil tarn difficile est 

Quin qnaerendo investigare possit.— Terence. , 

Now, let US indulge in a cosmical speculation. The 
universal world-stuff is scattered generally through bound- 

* Paris Acad. Sciences, June 18, 1883, Nature, xxviii, 205. See the Siemens 
theoiy further discussed in Comptes Renclus, Jan. 8, 1883, p. 79. Also by W. M 
Williams: Current Discussions in Science, ch. ii. 1882, Also, recently, by E. H 
Cook (Phil. jMag., 400-5, June, 1883. Amer, Jour. Sci., III,xxvi, 67-8, 140) and Dr 
Siemens' reply {Phil. Mag., July, 1883, Amer. Jour. Sci., Ill, xxvi, 146-7, Aug. 
1883). Siemens' late lecture at the Royal Institution may be found in Nature 
xxviii, 19-21, The whole theory, together with the various objections, is dis 
cussed in a small volume just published by Dr. Siemens, entitled, On the Con 
servation of Solar Energy^ London, 111 pp. 



66 COSMICAL DUST. 

less space. Perhaps, as Macvicar and Saigey* have 
suggested, this primordial stuff in an extreme state of 
attenuation, is the ether, the medium whose vibrations, 
according to Dr. Young, striking the retina, produce the 
sensation of light. Out of this semi-spiritual substance 
germinate then the molecules of common matter. It may 
be but varying modes of the ethereal atom as conceived 
by Young, which give rise to the sixty or seventy sorts of 
chemical atoms, whose more complex arrangements con- 
stitute the molecules which make up the molar aggrega- 
tions of ordinary matter. It may be, on the other hand, 
only a highly attenuated condition of ordinary matter, or 
matter in a state of ultimate dissociation. This character- 
istic world-stuff, born out of ether, in the depths of space, 
or however born, strewn through the depths of space, 
is acted upon by forces of attraction and probably of 
repulsion. The material particles, either as atoms, or less 
probably, as molecules, are drawn by mutual attraction 
into groups and swarms. Any central attractive force, as 
of a sun or planet, by causing the particles to move in 
converging lines, would cause them to become approx- 
imated, and ultimately aggregated. Thus, both mutual 
attractions and centric movements would tend to produce 
molar aggregations dispersed through space. But in the 
presence of two or more attractive centres, as in the 
present constitution of the cosmos, it is impossible that 
any mass shall fall directly upon its centre of attraction. 
A body A, Fig. 15, let fall a hundred thousand miles from 
the earth would not probably fall to the earth. Other 
attractions besides that of the earth would be felt by it. 
The resultant of these, the chief of which would be that 
of the sun and moon, must, in all probability^, deflect the 
body from a straight course toward the earth, as in the 
direction A F. Scarcely one chance in millions would 

♦Saigey: T/ie Unity of Natural Fhenomena. Translation, Boston, 1873. 



A THEORY, 



67 



exist, that the resultant of all the attractions should coin- 
cide with the line of descent to the earth. The idea 
implies, either that all the matter in the universe be 
arranged along one line coincident with that connecting 
the body with the earth, or that it be disposed with per- 
fect gravitative symmetry on opposite sides of that line. 
We must conclude that the falling body 
would be deflected from its course. A 
slight deflection would cause it to pass 
one side of the earth to B, and even to 
clear the earth's atmosphere. It would 
then move a hundred thousand miles on 
the side opposite to that from which it 
started. But instead of continuing to 
move in the same direction, the earth's 
attraction, while it tends to retard the 
movement along the receding line, B C, 
Fig. 15, is exerted obliquely to that 
line, so that after any given interval of 
time the body is at D' instead of D, 
and when its motion away from A is 
completely neutralized, the body is at 
C instead of C. It is now in the same 
relative position as when starting from 
A, but possesses a certain amount of 
motion in the direction of C C. As it 
begins, therefore, to descend toward E, 
its transverse motion carries it one side 
of E to D". But the transverse motion being constant and 
the descending motion accelerated in consequence of the 
increasing influence of the earth E, the path described will 
be a curve. As the transverse motion was generated while 
the body passed from B to C, it will be exactly destroyed 
in passing from C to D". Thus the body will return to A, 
after having completed the circuit of an elliptic orbit. At 




Fig. 15. Motion or 
A Body in the 

PRESENCE OF TWO 
OTHER BODIES. 



68 COSMICAL DUST. 

this point it will be in the same relative position as at C 
and independently of any external attraction, will proceed 
to describe an orbit the second time, and thus the process 
will continue indefinitely. The original deflecting force 
may indeed continue to act, and other perturbating influ- 
ences may intervene, and it is readily intelligible that 
subsequent perturbations may bring the body nearer to 
the earth, or increase the distance between them. In 
either case the velocity of the body will be changed. A 
perturbative influence might even be so adjusted in 
amount and direction as to bring the body to the earth. 

It appears, therefore, that in the actual disposition of 
the matter of the universe, every body would tend to cir- 
culate about every other body. The body whose attrac- 
tions are most powerfully felt would become the approxi- 
mate centre of actual orbits for those masses affected by 
such superior attraction. As the sun is the chief centre 
of attraction within the solar system, most of the matter 
within the limits of the system must circulate about the 
sun. But I see no reason why meteoric matter should not 
also circulate about the planets and satellites. 

The actual conflict of attractive forces is not, however, 
by any means, as simple as in the case supposed. In spite 
of the continual tendency of all bodies in space to describe 
orbital motions about each other, the conflicting attrac- 
tions are so infinitely diversified in amount and direction, 
and so variable with the varying distances of bodies, that 
the very fulfilment of the laws of motion results in a net- 
work of movements which is utterly incomprehensible, and 
must inevitably precipitate countless collisions of particles 
and masses. The smaller the mass relative to the masses 
which control its motions, the greater its liability to pre- 
cipitation. 

As to the ao-oregfation of cosmical matter, I have stated 
that, in addition to the mutual attraction of the molecules, 



A THEORY. 69 

the convergence of their paths toward centres of attraction 
must also tend to the formation of masses and swarms of 
masses and particles. We have then to picture indefinite 
space as pervaded by swarms of masses and particles of 
dark matter. Each mass or particle may, nevertheless, be 
separated by thousands of miles, from its nearest neigh- 
bor in the same swarm. I imagine these masses must be 
continually passing between us and the bright disc of the 
moon; but each mass is so small relatively, that the light 
of the moon is not sensibly affected by it. The same is true 
of any heavenly body presenting a sensible disc, like the 
planets. But the fixed stars are so remote that, by per- 
spective, they are reduced to points of light. They must 
be occulted then, by every small mass of dark matter 
passing between them and us. All small masses within 
hundreds, and perhaps thousands, of miles of our eyes 
would probably produce sensible effects upon the light of 
mere luminous points, unless disguised by the effects of 
atmospheric refraction. Were there not reasons for sup- 
posing the twinkling of the fixed stars a mere atmospheric 
phenomenon, it might be worth while to consider whether 
it may not be due to occupations by meteoric matter, 
especially as the disc-presenting planets are free from 
scintillation. On this theory, however, a planet so remote 
as to present no sensible disc should also twinkle to some 
extent. 

Swarms of small masses of dark matter may therefore be 
conceived as circling in numberless orbits and in all direc- 
tions about the principal bodies of the solar system, but 
in much the greatest number about the sun. All the 
moving bodies of our system must be continually pelted 
by these cosmical atoms, and the aggregate result of these 
collisions must, in thousands or millions of years, affect 
their motions. Supposing the motions of the cosmical 
atoms to have no prevailing direction, it is evident that 



70 COSMICAL DUST. 

the motions of the planets, satellites and comets of our 
system would cause them to meet more of these atoms 
than the total number which would overtake them. The 
result would therefore be a resistance to the move- 
ment of these bodies, and the effect of this would be 
an acceleration of their motions and a shortening of 
their periods. I venture the opinion that this cause is 
a more efficient resistence than the supposed ethereal 
medium. 

This simple conclusion is very fruitful of deductive re- 
sults,* as Professor M. H. Doolittle has shown. The resis- 
tance of an ethereal medium has always been regarded by 
many ph^^sicists as an inadequate explanation of the come- 
tary phenomena which hav^e been appealed to as evincing 
the existence of a universal ether. But the dense distri- 
bution of cosmical matter may fairly be assigned as a 
physical explanation of the following otherwise perplexing 
phenomena: 1. The acceleration of all orbital movements, 
including those of comets, and especially that of the inner 
satellite of Mars, which revolves about its primary in a 
little over seven hours, while the planet revolves on its 
axis in about 24 hours, thus causing this moon to rise in 

* It was indepeudentlj' enunciated by the writer in a public lecture, De- 
cember 3, 1877, at Syracuse, New York. The substance of the lecture was 
reported in the Syracuse papers of December 4. The lecture was subsequently 
repeated, December 7, at Groton, New York; January 4, at Pulaski, New York; 
February 5, at Cleveland, Ohio; February 12, at Richmond, Illinois, and Febru- 
ary 16, at Lebanon, Ohio. I find that a similar conception was enunciated at an 
earlier date, by Rev. S. Parsons, A.M. " No doubt the comets and all other 
bodies meet with cosmical matter, which is 'diffused profusely throughout the 
universe,'' according to the observation of Laplace. In the course of ages this 
diffused matter must present a sensible resistance to the motion of bodies 
through the universe." After citing the abundance of meteoroidal bodies, 
he added: "Such an amount of resistance would be sufficient to change the 
earth's orbit from an extreme oval into its present shape" (Methodist Quar- 
terly Heview, January, 1877, p. 135). The conception was subsequently, though 
independently, put forth by Mr. M. H. Doolittle, in a paper before the " Philo- 
sophical Society" of Washington (New York Daily Tribune^ March 6, 1878. 
See a further communication in the same, April 6, 1878) 



A THEORY. 71 

the west and set in the east.* 2. The irregularities in 
the motions of comets, especially noted in Encke's; since 
meteoroids, not being uniformly distributed, would not 
offer uniform resistances. 3. The want of coincidence be- 
tween the planes of the equators of the various bodies of 
the solar system, and between these and the planes of 
their orbits. This is a group of facts requiring for their 
explanation the exertion of some force from without the 
svstem. 4. The eccentricities of the planetary orbits. 

While, however, the phenomena mentioned under the 
last two heads may possibly be best explained on the 
hypothesis of meteoroidal resistance, it is admitted that 
perturbative attractions must probably be cited for the 
same purpose. f 

Returning to the consideration of the constituent masses 
or particles out of which swarms of cosmic bodies would 
be constituted, it is manifest that each mass or particle 
will eventually dispose itself, under the fixed action of the 
forces of matter, in some definite order. It is manifest 
also, from what has been said, that each swarm will have a 
progressive motion along a path having the essential char- 
acter of an orbit around some dominant centre of attrac- 
tion. If, as seems to be the fact, an ethereal medium, or 
any condition of interplanetary matter, exists in space, it 
opposes the movements of these swarms, by opposing the 
motion of each constituent mass. But the smaller masses 
— the particles and molecules — would feel this resistance 
to the greatest extent. They would therefore fall behind 
the heavier masses and would be most deflected toward 
the attracting centre. The smallest particles would be 
driven farthest to the rear, and dispersed farthest from 
the orbit of the train, along the side turned toward the 

*I shall hereafter show that the solar tidal influence is also adequate to 
produce such a result. 

t These two classes of phenomena are considered in Part II. 



72 COSMICAL DUST. 

principal attraction. The swarm would present an elon- 
gated form in which the larger and heavier masses would 
move foremost, and nearest the line of the orbit — that is, 
near the exterior skirt of the area covered by the general 
swarm, as in the case of the bolide at Queengouck (Fig 
4) — while the smaller ones would follow, in graduated 
succession, in a long train which would present a fan-like 
expansion lying mostly on the inside of the path of the 
principal masses. 

This, it may be conceived, is the mode of aggregation 
of these cosmical matters in the depths of space. Of course 
the attractions which control them are feeble; their move- 
ments are slow, the resistances are relatively inconsider- 
able, and the elongation of the swarm is correspondingly 
inconspicuous. What I have described is a tendency 
which would be present. Sometimes the controlling at- 
traction would be only another cosmical swarm. The two 
swarms would revolve similarly about their common centre 
of gravity; while prolonged resistances would cause their 
slow approximation and final coalescence at the common 
centre of gravity. Sometimes the controlling attraction 
would be exerted by a distant sun, around which it would 
slowly move, continually gathering up additions of matter 
from the wide fields of space. 

In most cases, all controlling attraction would be feebly 
felt. These clouds of cosmical dust would float practically 
poised in the midst of space, and would gradually grow 
by the continued accession of new matter. Some of them 
would become aggregates of large dimensions, and their 
attractions would be distinctly felt by other aggregates. 
There would be a tendency of such aggregates to approach 
each other. They might possibly approach along a straight 
line, but more probably some third aggregation, or some 
distant sun, would deflect them into orbits about their 
common centre of gravity, in which, by prolonged collis- 



A THEORY. 73 

ions of cosmical matter, they are brought to ultimate 
coalescence with each other. Or some other attractive 
disturbance affords such a resultant of actions as may bring 
them more directly together. When these larger aggre- 
gations of world-stuff come together, the result is an 
aggregation approaching the dimensions of the Her- 
schellian nebula. To these attention will be directed pres- 
ently. 

There are other aggregations of very moderate magni- 
tude which chance to fall under the influence of some dis- 
tant sun, toward which they move through a series of 
ages — deflected, however, by lateral attractions into orbital 
paths. In the nearer neighborhood of some great attrac- 
tive centre, the velocity of one of these swarms is acceler- 
ated. Its form becomes more elongated. The internal 
movements of the parts become more vigorous; collisions 
are sharper, and flashes of light are evolved, and the pos- 
terior train is expanded. Further influence exerted by 
the central body increases all these consequences. The 
head of the swarm becomes permanently luminous. The 
long gathering swarm is now a comet. It may have already 
entered within the precincts of our solar system. It moves 
toward the neighborhood of our sun with ever-increasing 
velocity and brilliancy and length of train. Meantime the 
mysterious power — apparently repulsive — which the sun 
exerts upon its constituent matter drives off infinitesimal 
particles, but intensely luminous, to constitute that char- 
acteristic appendage known as the tail. This must be 
distinguished from the train just mentioned. It rushes 
on; it probably misses collision with the sun, is reined 
back, and speeds by virtue of its acquired velocity, nearly 
in the direction of a tangent to the perihelion curve des- 
cribed, into the remoter regions of our system. 

When the cometary aggregation comes from an indef- 
inite distance beyond the confines of our system, moved 



74 COSMICAL DUST. 

only by the sun's attraction, it acquires such velocity 
as to move in a parabolic curve, and hence, when it re- 
cedes from the sun it can never return unless its path is 
changed by some perturbative action. It is extremely im- 
probable that the mass should move with precisely this 
velocity. The planets of our system, especially when the 
comet passes in their vicinity, distinctly impress its mo- 
tions. Sometimes the action is such as to accelerate its 
velocity, and it then whirls around the sun and departs, 
never to return, along a hyperbolic path. These non- 
periodic comets probably proceed across the void which 
separates our system from neighboring systems. They 
escape beyond the influence of powerful attractions and 
correspondingly lay aside their cometary characteristics. 
Some of them probably unite with other nebular aggrega- 
tions. Others, escaping through the labyrinth of attrac- 
tions, move on until another sun calls them to itself. The 
former experience may then be repeated; and the com- 
etary body may perchance travel from system to system 
weaving the realm of material existence into a unity. 

But the cometary body which ventures into our system 
may be still differently impressed by the attractions of the 
planets. Its motion may be retarded. From the moment 
when its velocity is less than that which it would acquire 
in falling from an infinite distance, it begins to move in an 
elliptic path. It is destined to come around again to the 
same point. It is a periodic comet. Its aphelion is likely 
to be located near the region where its nevt path was de- 
termined. The largest planets are of course most likely 
to exert this determinative influence. Hence, of the peri- 
odic comets, nearly all have their aphelia near the orbit of 
some one of the major planets. Thus there is a Jovian 
group and a Saturnian group. Most of the periodic 
comets move around the sun in the same direction as the 
planets; while, of the whole number of comets recorded, 



A THEORY. 75 

about half have moved in the opposite direction. This 
circumstance is unexplained, but it must be connected with 
the direction of the planetary motions, or with a general 
vortical movement of the ethereal fluid and interplanetary 
matters, which would exert increased influence on the 
slackened motion of comets turned into elliptic orbits. 

But now, the comet, domiciled within the system, is 
subjected to constant perturbative torments. Its eccentric 
orbit carries it across the paths of the planets, and it is 
pulled successively in various directions. The enormous 
stress experienced in passing the close vicinity of the sun 
throws it into a state of violent internal commotion. In a 
body whose parts are so incoherent, dislocation and disin- 
tegration begin. A constituent portion struck by another 
has its velocity increased, and it tends to move tangentially 
away from the sun; the part striking has its velocity 
diminished, and it tends to move nearer the sun. The 
effect is to disperse the parts. Wrenched and racked by 
the distracting pulls of the sun and planets, it begins to 
go to pieces. We have seen comets going to pieces before 
our eyes. The process may be slow, but it is real and pro- 
gressive. The train elongates and attenuates, under the 
influence of the prolonged acceleration of motion experi- 
enced on entering our system; and at length the disinte- 
gration of the parts proceeds so far that the nucleus loses 
its luminosity and the swarm of constituents continues for 
a time to move about the sun as a meteoroidal train. Ever 
elongating, it may stretch at last quite around its orbit. 
This extending train, intercepted by planetary atmospheres, 
rains down its substance in showers of "shooting stars;" 
but otherwise, it continues gradually to approach the sun, 
and is ultimately gathered as " solary fuel " in the central 
fire of our system.* 

*The bearing of Von Reichenbach's researches on meteorites and shooting 
stars ought to have been earlier noticed. He finds all meteoric stones to be com- 
pounded of parts — hundreds or even thousands of mechanically separate constit- 



76 COSMICAL BUST. 

The theor}' which claims a continuity between comets 
and meteoroidal trains, encounters, it must be confessed, 

uents. Ordinary meteoric stones are aggregates of smaller meteoric stones. 
Both the larger and the smaller are composed of substances whose arrangement 
always follows a certain order. In the centre are oxidized substances, such as 
sihcates; upon these are layers of sulphurets. graphite, and finally of native iron. 
If either class of constituents is absent, the remaining ones follow the fixed order. 
Thus there has been a growth; and the oxides or stonj- constituents are older 
than the metallic. So, also, the smaller constituent meteorites are older than the 
conglomerates formed by their aggregation. 

The formation and cementation of the parts has not been effected through 
the agency of a fusing heat. If so, the heavier iron would not have settled 
around the lighter olivine, nor would graphite sustain its actual relation to mag- 
netic pyrites. The primitive olinne was surrounded by a primitive iron-gas. 
The primitive condition of all the substances was gaseous— not nebulous. Under 
conditions once existing, the oxygen was active and entered into its combina- 
tions, forming the primitive stony nuclei of meteorites. Later, the sulphides, 
and then the graphite, were isolated and deposited. Finally, either because the 
oxygen was exhausted or inactive, or because the work was carried on in a dif- 
ferent laboratory, the unosidized iron was deposited in layers and fillings of all 
the interstices. All these layers are crystalline. 

Thus, before the existence of the meteorites which fall from heaven in our 
time, there must have been a certain period in which smaller, finer, and more 
numerous meteorites {Meteontchen) were produced — as "mere dust, starch-flour, 
sand, grains to the size of hail-stones'' — these in their microscopic structure 
composed of still minuter bodies. 

Shooting-stars and fire-balls are only meteoric bodies, so small as to be dissi- 
pated in our atmosphere on their way to the earth. These bodies, large and 
small, float in space, and by degrees are drawn to the earth. In the course of 
ages the}' must contribute important additions to the earth. INickel and cobalt, 
he explains, are found in all our soils. They are not afforded by the rocks from 
which soils are chiefly formed; but they are characteristic constituents of 
meteorites. 

The constituent parts of meteorites present evidence of collision and attri- 
tion. They are rounded, as well as angular and subangular. The very dust 
worn from them (Reibsel) is cemented together with the larger kernels and balls 
by means of nickeliferous iron. When ignited in our atmosphere, they are 
again dissipated in vapor. "Und man hatte sich dieses als eiuen feinen Regen, 
als einen unsichtbaren Duft zu denken, der in ausserst geriugcr Menge und in 
hochst feiner Yertheilung ohne Unterlass sich aus der Atmosphare auf unsere 
Meere, Wiilder und Gefilde nicdersenkf" 

It is at once apparent how the facts here cited quadrate with the theory set 
forth in the text. 

These speculations of Von Eeichenbach are embraced in a series of memoirs 
as follows: Ueber die ZeUfolge und die Bildungswtise der ndheren Bestand- 
theile der Meteoriten, Poggendorff's Annalen. cviii, 452-65, 1859; Meteoriten in 
Meieoriten, id., cxi, 353-86, 1860: Meteoriten und Stemschnrtppen, id., cxi, 387-401, 
1860; Die Sternschnuppen in ihren Beziehungtn zur Erdoberfldchen^ id. cxziii, 
368-74, 1864. 



A THEORY. 77 

some difficulties not yet fully explained. The common 
representation is that the train of the meteoroidal swarm 
is to be identified with the tail of the comet; but this is 
evidently inadmissible, because the comet's tail precedes 
during the retreat from the sun, and because the velocity 
implied in the distant parts of the tail while passing peri- 
helion is entirely inadmissible as an actual translation of 
matter, and perhaps also, in consequence of its considera- 
ble luminosity at great distances from the sun. Again, 
the luminosity of the head itself, at a distance as great as 
Mars or Jupiter from the sun, cannot be due to the intense 
heat of the sun's rays, as might be the case at perihelion. 
The amount of collision among the parts, in an aggrega- 
tion containing so little matter as a comet, can with diffi- 
culty be conceived as imparting the permanent luminosity; 
and the query arises whether the phenomenon is not due 
to some other action than heat. It is supposable that the 
light of the tail is wholly reflected, as we know most of it 
is, in the nearer vicinity of the sun. The nuclei are well 
known to contain incandescent gases when they have been 
examined on their visit, to the sun's neighborhood; but one 
would expect masses so limited in amount to lose their 
thermal luminosity in receding toward their aphelia.* 

The phenomena of the tail, especially in the vicinity of 
aphelion, are such as would result if we could conceive the 
nucleus of the comet surrounded by an aura extending on 
all sides as far as the remotest limits of the tail, and could 
recognize the tail as merely a luminous shadoic cast by the 
nucleus in intercepting certain radiant energy proceeding 

* One is reminded, in this connection, of the analogies between cometary 
tails, the streamers of the aurora borealis and the trains of radiant matter in the 
tubes employed by Professor Crookcs (see references, p. 49). Without affirming 
a '• fourth state of matter," or even the doctrine of the continuity of states, it is 
apparent that the attenuation of the medium in which the phenomena of "ra- 
diant matter"' are revealed, is quite analogous to that of the medium in which 
the northern streamers dance, or in which the tails of comits execute motions of 
such mysterious velocity. 



78 COSMICAL DUST. 

from the sun.* Perhaps, after all, the theory is the most 
plausible one which contemplates the tail as a vapor of 
some unknown constitution, perpetually driven off by some 
mysterious repulsive power of the sun, perhaps electric, 
growing more intense with diminished distance. The tail 
would be, therefore, not a material form moving with the 
comet, but something perpetually renewed, while the older 
and more distant emanations disappear from visibility. 
M. Faye, in this view, compares the comet's tail to the 
smoke rising from the pipe of a transatlantic steamer, 
which, though continually changing molecularly, is the 
same phenomenon all the way from Havre to New York. 

Thus we glimpse in outline the cosmic conception which 
forms the ground of the reasonings and speculations of the 
present work. The world in which we live is to be ac- 
counted for, and the method of its evolution explained. 
Geology undertakes to write some chapters of its past 
history; but a true geology, in a broader sense, will 
unfold many other glowing chapters, which mere induc- 
tive science could never make known. We take up the 
details of the first chapters of inductive geology with the 
feeling that much has been left out. They present only 
the beginning of the last act of the drama. But our 
intelligence presses back in search of a real beginning of 
the world; and even if scientific inquiry is doomed to 
failure in its search for an absolute beginning, it is a 
noble impulse and an inalienable prerogative which sanc- 
tion the effort to press as far as possible toward the abso- 
lute beginning. I doubt if we can at present fix upon a 
starting point antecedent to that diffused chaotic condi- 
tion of world-stuff of which so many glimpses have been 
revealed to the mind's eye. I strongly believe we have 

*See W. A. Norton on comets in Ainer. Jour. Sci., II, xxvii, 86, 103; xxix,79, 
383-6. See also Bredechin's researches on the tails of comets, Annales de I'Ob- 
servatoire de JIoscou, vols, iil-vi, and M. Faye's memoirs, Comptes Rendus, Aug. 
1 and 8, 1881. 



A THEORY. 79 

caught glimpses of the mode of formation of world germs. 
It remains then, to trace their development, their maturity 
and their decadence. This will lead us to the study of 
nebular life, and the nature of the continuity existing 
between nebuhe, suns and planets; and to contemplate 
finally those ulterior planetary conditions which disclose 
the data of a geology of the future, and complete the 
natural cycle of cosmic existence. 



CHAPTEE II. 
NEBULAR LIFE. 

Que dire de ces espaces immenses et des astres qui les remplissent? Que 
penser de ces etoiles qui sont sans doute, comme notre Soleil, des centres de 
lumiere, de chaleur et d'activite, destine's conime lui, a eutretenir la vie d'une 
foule de cre'atures de toute espece?— Le padre Secchi. 

THE irresolvable nebula, as I have endeavored to indi- 
cate, are probably nothing but stupendous examples 
of meteoric or cosmical clouds which have become heated 
to such an intensity that their matter, or some of it, exists 
as vapor, though it is not necessary to suppose that the 
portions subjected to observation sustain a temperature of 
relatively high intensity. At the same time, such is their 
enormous mass that their interiors must be compressed to 
many thousand times the density of the exterior por- 
tions. These prodigious accumulations may have been 
gathered, by the mutual attractions of the parts, from 
wide contiguous fields of space. They are not drawn out 
into meteoric rings or partial rings surrounding our sun, 
because they are so immensely remote as to be little 
affected by the solar attraction, and are relatively so vast 
as to possess controlling power of their own. They have 
not formed meteoric rings around other suns, because 
they are equally remote from them and equally exceed 
them in mass. According to the conception from w^hich 
we reason, the nebular aggregations discernible within 
our field of vision — both resolvable and irresolvable — lie 
dispersed through unlimited space. Many — perhaps most 
or even all of them — float within the bounds of that 
starry universe whose nearer members constitute our vis- 

80 



N"EBULAR HEAT. 81 

ible firmament. But if with Herschel we set limits to 
our starry firmament, we may readily believe that many 
of these nebular aggregations lie far beyond the distance 
of its remotest star. According to Father Secchi, the 
depths of the cosmos are unfathomable. All the stars 
constituting the firmament surrounding our sun are but a 
patch of the boundless Milky Way, and if seen from a cer- 
tain distance would appear only as a white spot in the 
Milky Way itself. In any view of the relative positions of 
the nebulag, the cosmic organisms of infinite space lie separ- 
ated by such enormous intervals that while one of these 
clouds of world-stuff must feebly feel the attractions of 
other material masses, it may be regarded as practically 
removed from their influence. We have now to inquire, 
what will be its behavior ? 

§ 1. NEBULAR HEAT. 

1. Heat Produced hy Befrigerative Contraction. — At 
an earlier period, we must assume, the gathering nebulous 
matter was cold and non-luminous. Accordingly we may 
conjecture that countless germs of future nebulae exist in 
space, which have not yet been discovered, because not yet 
heated. By what means a nebulous mass becomes so 
heated as to be self-luminous, is supposed by some physi- 
cists to be demonstrated by the uniform evolution of heat 
in every body which undergoes condensation by pressure. 
Helmholz, Peirce, Sir William Thomson and others have 
calculated the amount of heat which must be evolved dur- 
ing the condensation of the sun from such a volume as 
would fill the orbit of Neptune.* Young and others have 
suggested that the heat of the incandescent nebula whose 

*Mr, Maxwell Hall has calculated that to supply the sun's loss of heat 
from radiation, it is only necessary to contract 39.15 metres a year. This would 
require 18,263 years to effect a shrinkage of one second in the sun's diameter 
(Monthly Notices, Astronomical Society, 1874, 237) . 
6 



82 KEBULAR LIFE. 

condition is revealed by the spectroscope, has been liber- 
ated during a process of spontaneous condensation. If 
this explanation is legitimate and sufficient, it is unneces- 
sary to seek farther for the cause of nebular luminosity. 

The explanation, however, seems to be a suitable sub- 
ject for examination. At first glance it would seem to 
contradict reason. It is quite apparent that if the nebula 
is internally in equilibrio, such heat would be evolved if 
the condensation were effected by the application of force 
from loithout — as the air is heated in a condensing syr- 
inge, or iron under a hammer. But a spontaneous con- 
densation excludes the application of extraneous force. 
It means a condensation under the influence of forces resi- 
dent in the mass. These forces as far as this question is 
concerned, are central attraction, molecular attractions 
and repulsions, and heat. At a given moment, in a 
nebula internally in equilibrium, the central attraction of 
the parts is exactly balanced by the repulsive or expansive 
force due to the amount of heat belonging to the body. 
Without any change in the relative intensities of these 
shrinkage and expansive forces, the volume of the nebula 
must necessarily remain unchanged. Its temperature, of 
course, remains unchanged. If, at any moment, its tem- 
perature is above that of surrounding space, it must radiate 
a portion of its heat. A certain amount of contraction 
exactly corresponding with the amount of heat lost, will 
ensue. The equilibrium between the reactionary and the 
central attractive forces is restored, and. the volume must 
remain unchanged until farther loss of heat takes place. 
Thus, the condensation, supposing always that the aggre- 
gative process is completed, can only respond to loss of 
heat. No condensation can take place except as a conse- 
quence of such loss. The condensation, therefore, cannot 
increase the heat. If, during a process of condensation, 
the temperature is raised, this, in the light of the princi- 



NEBULAR HEAT. 83 

pies stated, must be the consequence of force applied 
from without. 

Obviously, there is a period in the aggregation of a 
nebula during which the central attraction may be re- 
garded as crowding the constituents together; and during 
this period, heat would be developed. An equilibrium 
being attained between this attraction and the repulsive 
forces, the nebula will have reached the normal state at 
which its evolutions begin. Some nebulae, undoubtedly, 
exist in the prenormal state, and may be growing heated 
by condensation — but it has not seemed to me that 
all nebuLne must be supposed in this condition. Perhaps 
the o'reater number must be in some sta^e in which the 
condensation is conditioned and measured by the cooling. 

Professor Simon Newcomb in his admirable work on 
*' Popular Astronomy " (pp. 507, 508), speaking of the 
possible cause of the perpetuation of the sun's heat, says: 

"As his globe cools off'it must contract, and the heat 
generated hy this contraction will suffice to make up 
almost the entire loss." That is, cooling causes contrac- 
tion, and contraction causes heat; therefore cooling causes 
heat. But further: " By losing heat a gaseous body con- 
tracts, and the heat generated by the contraction exceeds 
that which it had to lose in order to produce the contrac- 
tion."* This curious paradox was rendered rational by a 
learned investigation published by Mr. J. Homer Lane, of 
Washington, t the gist of whose paper is thus summarized 
by Professor Newcomb: "If a globular gaseous mass is 
condensed to one-half its primitive diameter, the central 
attraction upon any part of its mass will be increased four- 
fold, while the surface upon which this attraction is exer- 

* Then certainly the body is growing hotter and consequently expanding 
while it contracts from cooling!— unless, meantime, the surplus heat is lost by 
radiation. 

\ American Journal of Science for July, 1870. 



84 N"EBULAR LIFE. 

cised will be reduced to one-fourth. Hence the pressure 
per unit of surface will be increased sixteen times, while 
the density will be increased only eight times. Hence if 
the elastic and gravitating forces were in equilibrium in 
the primitive condition of the gaseous mass, its tempera- 
ture must be doubled in order that they may still be in 
equilibrium when the diameter is reduced one-half." 

For the sake of further elucidating this curious paradox 
let us enunciate the points in the following form : 

(1.) If the diameter is reduced one-half, the density is 
eight times as great, since the same matter is compressed 
into one-eighth the volume. 

(2.) The intensity of attraction, and therefore the total 
attraction, at the new surface, is four times as great, since 
the same amount of matter attracts at one-half the former 
distance from the centre of gravity. 

(3.) But the new surface is only one-fourth the original 
surface; hence each unit of new surface must receive six- 
teen times the attraction (pressure) of a unit of the 
original surface. 

(4.) If the pressure is sixteen times as great, and the 
density is only eight times as great, the elastic force to 
equilibrate the excess of pressure must be twice as great. 

Now, if that elastic force is wholly heat, the shrunken 
body must have twice the heat of the original body; and 
that is what the contractional theory, as commonly stated, 
concludes; and in this way a surplus of heat may be radi- 
ated, and still a constant or even increasing temperature 
maintained. 

But the new body has not twice the heat of the old 
body, since, necessarily, a constant radiation of heat has 
been taking place. 

If, by hypothesis, the original body has shrunken to 
half its dimensions, and by observation, some of its heat 
is known to have been lost, the new body will be half the 



NEBULAR, HEAT. 85 

diameter of the old, without having twice the amount of 
heat. That is, the elastic force which equilibrates the 
excess of j^fessure is 17% part at leasts something besides 
heat. 

This is also evident from the consideration that the 
body is supposed to shrink simply in consequence of cool- 
ing; and the supposition of an increase of heat is in con- 
flict with the assumed premise. A body cannot be growing 
hotter in consequence of a shrinkage produced by growing 
colder. It may have some of its heat restored, and thus 
its cooling retarded. To assume that the temperature is 
not lowered in correspondence with a decrease of volume 
when the pressure is constant, is in conflict with the well 
established law of Charles. 

But it is assumed that the heat developed by shrinkage 
is lost through radiation in the meantime. If only the 
excess developed is lost, the body remains of the same 
temperature as at first, and, therefore, is not cooling, as 
the premise demands. 

Also, if the excess, or more than the excess of heat is 
radiated, then there is less elastic force in the form of 
heat than in the original body, while the reasoning requires 
twice as much. 

It seems, therefore, that the doubled elastic force 
required in the shrunken body to equilibrate the increased 
pressure must be something besides heat. May it not be 
simply a repulsion among the molecules, which varies 
according to some law of the distance? 

Now, the following seems to me to be a correct sum- 
mary statement of the whole case: 

(1.) The falling together of the particles and masses 
will generate heat; and the generation will progress as 
long as the parts continue to descend toward the common 
centre of gravity. 

(2.) The heat thus developed will be active, sensible 



86 XEBUI^AR LIFE. 

heat. The sensible temperature resulting must, however, 
be discriminated, as always, from the total thermal potency 
in the body, 

(3.) The centric movement of the parts will cease when 
the elastic forces become equal to the gravitating tendency 
of the parts. The nebula is then, disregarding the effect 
of progressive radiation, in a state of internal equilibrium. 

(4.) Subsequent loss of heat will permit the parts again 
to fall together, until their approximation, or in other 
words, the work done by the descending parts, develops 
an increased amount of elastic force, partly heat, which 
will again equilibrate gravity even at its now increased 
intensity. 

(5.) The loss of heat diminishes the total amount of 
heat, and diminishes the temperature; but the descent of 
the parts will necessarily develop a new amount of heat, 
and partially restore the temperature and volume. 

(6.) The former temperature cannot be completely 
restored, for that was a temperature which maintained 
the mass at the volume which it had before the contrac- 
tion; and by hypothesis, contraction is a fact. 

(7.) As the newly developed heat must fail to equili- 
brate the newly increased pressure, the equilibrium must 
be completed by some reactionary force which would 
exist at absolute zero of temperature. 

(8.) The actual volume will lie, therefore, between the 
original volume and that which would have resulted if 
contraction had not developed heat; and the actual tem- 
perature will lie between the original temperature and 
that which would have resulted if no heat had been 
developed by contraction. 

(9.) It is true, then, that contraction develops heat, and 
that its development delays final refrigeration; — that is, 
the progress toward final refrigeration is not as rapid as 
the amount of radiated heat implies. But it is not true 



NEBULAR HEAT. 87 

that contraction (from cooling) can have developed the 
whole amount of heat at any time existing in the mass, 
or can even maintain a body at a constant temperature. 

2. Changes in the Forms of Nehulm. — From this 
quite abstruse question let us return. If we have to con- 
clude that a shrinkage or condensation in a gaseous mass 
whose parts are maintained in a state of mutual equilib- 
rium is physically incapable of developing the heat which 
we find existent in nebulae, then we have to inquire, what 
is the external cause which develops, maintains or increases 
the heat of a nebulous mass in space? 

As I have stated, we may reasonably assume the cos- 
mical dust promiscuously distributed. But mutual attrac- 
tions would, sooner or later, result in conglomerations of 
relatively moderate size. This process would be accom- 
panied by a transformation of gravitational energy into 
thermal, and this would be continued until the internal 
elastic forces should be able to equilibrate the gravita- 
tional forces. The nebula would have assumed its normal 
condition. Every nebulous conglomeration would still be 
attracted by any other — both the larger and the smaller. 
The process of conglomeration would, therefore, tend to 
continue indefinitely. Those immense nebulae would finally 
be developed which have attracted the attention of astron- 
omers. The larger masses having drawn to themselves all 
the smaller masses in their several regions of space, the 
intervening spaces would seem to be comparatively free 
from nebulous matter. 

Now, I would suggest that the process of conglomera- 
tion may explain the irregularities in thefor)ns of certain 
nebulae. The protuberant portions, the salient angles, the 
denser bands, the luminous spots, may all be conceived as 
precipitated nebulous masses which have not yet had time 
to become completely coalesced; or they are nebulous 
masses which have been pushed out of symmetry or homo- 



88 XEBULAR LIFE. 

geneity by the impact of a foreign mass. We have gazed 
on those irregular forms, like the nebula in Orion, and the 
Magellanic Clouds, and, mindful of the law of matter by 
which, when free to move upon itself, it assumes the 
spherical form, we have deemed it mysterious that such 
irregularity could persist. Now, on the theory just enunci- 
ated, the irregularity must arise; but there is nothing to 
cause it to persist. The irregular nebula must be in pro- 
cess of assuming some symmetrical shape. Its destined 
shape is not already assumed, because the history of its 
evolutions began in finite time. The nebula has not yet 
had time sufficient to undergo its changes. Its destined 
evolution must, therefore, be in progress at this moment. 
Now, it is gratifying to be able to announce that changes 
have been noted in nebular phenomena. " Some nebulae 
have vanished; others have appeared where formerly no 
nebulosity had been recognized." Not a few changes have 
been witnessed in the forms of nebulae. The Magellanic 
Clouds, according to Sir William Herschel,* have under- 
gone important changes during a human lifetime. The 
great Nebula in Orion (Figure 6) is now generally admit- 
ted to be in process of change. f The nebula surrounding 
the remarkable variable star Eta Argus is subject to great 
changes.! The Omega Nebula (H. 2,008) through the 
careful researches of Professor E. S. Holden, is shown to 
be probably undergoing internal changes. § The various 

*Herschel, Phil. Trans, 1811. So, also, Sir John Herschel: "Speaking 
from my own impressions, I should say that in the structure of the Magellanic 
Clouds it is really difficult not to believe we see distinct evidence of the exercise 
of such a power of aggregation."— .4<i(ire5s, British Association, 1845. 

tSchellen: Spectral Analysis, 371; Sir W. Herschel, Phil. Trans., 1811; 
Otto Struve, Monthly Notices Astronom. Soc, London. March 14, 1856, vol. xvi, 
p. 139; Gautier, Archives des Sciences Physiques et Naturelles de Geneve. 18fi2, 
translated in Smithsonian Report, 1863, 299; Secchi, Comptes Rendus, Ixv, p. C43, 
Ixvi, 63. 

X F. Abbot, Proc. Roy. Astron. Soc, Nov. 13, 1863; Am. Jour. Set., II. xxxvii, 
294-6. 

§ Holden : On Supposed Changes in Nebula M. 17, Am. Jour. Sci., Ill, xi, 341- 
61, May, 1876. 



NEBULAR HEAT. 89 

drawings of this nebula, from that of Herschel in 1833 
to that of Lasell in 1862 (Fig. 16), and that of Trouvelot 
and Holden in 1875 (Fig. 17), seem to indicate that the 
eastern or omega-shaped portion of the nebula has under- 
gone considerable change in respect to the stars in closest 




Fig. 16.— The Omega Nebula. Fuom a Drawing by Lasell in 1862. 

contiguity to it. Professor Holden says: '"These draw- 
ings show that the western end of this nebula has moved 
relatively to its contained stars from 1833 to 1862, and 
again from 1862 to 1875, and always in the same direc- 
tion." Meantime the conspicuous "streak" or wing ex- 
tended toward the east has not moved in reference to the 



90 



NEBULAR LIFE. 




NEBULAR HEAT. 91 

stars. The parts of this nebula are, therefore, in motion 
with reference to each other. The Trifid Nebula has been 
shown by the same investigator * to possess a proper 
motion in reference to the stars. This nebula consists of 
three nebulosities separated by dark passages, as shown in 
Fig. 18. In the middle of the intervening space, from 




Fig. 18.— The Tripid Nebula, 
From a Draaving by Trouvelot. 

1784 to 1833, was situated a distinct triple star; but 
"from 1839 to 1877 the triple star was not centrally situ- 
ated between the three nebulosities," but involved in one 
of them.f 

* E. S. Holden, Am. Jour. Sci., Ill, xiv, 433-58. 

t On the motion of nebulae in the line of sight, see W. Huggins, Froc. Royal 
Soc, March, 1874. Seven nebulae observed indicate a motion in reference to the 
earth ranging from one to fourteen miles a second. 



92 KEBULAR LIFE. 

We may rest assured that fleecy masses like the nebulae, 
when presenting- forms as unsymmetrical as some of them, 
cannot be reposing in a state of finality.* We may 
wonder that these changes should be so slow that the 
nebula seems almost in a fixed condition. That apparent 
slowness of change, we may be certain, is a consequence 
of the inconceivable remoteness of those bodies. The 
star known as 1830 Groombridge is moving through our 
firmament at the rate of 200 miles a second; yet it re- 
quires 123 years to move over an angular space equal to 
the diameter of the moon. The diameters of some visible 
nebulae are probably greater than the distance which sep- 
arates us from the nearest star. Motion in masses so 
immense and so remote must necessarily seem deliberate. 
The earth takes twenty-four hours to turn over; the sun 
requires twenty-five days; a flea needs but a small fraction 
of a second. The moon revolves around its orbit in 
twenty-seven days, but Uranus consumes the time of 
three generations of men. Yet the diameter of the orbit 
of Uranus may easily^ be less than the space separating 
two distinguishable points of star-dust in a resolvable neb- 
ula. I think, therefore, we are not stretching the physi- 
cal probabilities in attributing the irregularities of the 
nebulfe to the process of conglomeration; and in antici- 
pating that the shapeless nebula in Orion will one day 
have assumed a symmetrical form. 

3. Heat Arising from the Aggregative Process. — The 
thought must already have suggested itself to the reader 
that the process of conglomeration affords an explanation 

* For mention of other supposed changes, see the memoir of Gantier, 
already cited. On the general question of nebular changes see Arago; Astro- 
nomie 2)op}daire. In some instances changes of brightness have been observed 
which are far more striking than any observed changes of form. The small 
nebula in Taurus, discovered by Hind iu 1852, had disappeared in 1861, and was 
not again visible till 1868, after which it again disappeared. So conversely, the 
temporary star discovered by Dr. Schmidt in the Swan, gradually faded into the 
appearance of a planetary nebula. 



NEBULAR HEAT 93 

of the intense heat which vaporizes its substance, and 
causes it to yield a spectrum of bright lines. As the sud- 
den compression of a portion of atmospheric air yields 
heat sufficient to ignite tinder, or fuse and volatilize a de- 
scending meteor-mass, so the precipitation of one planet 
upon another would liberate sufficient heat to reduce them 
both to a state of fusion, or even of vapor. Still more 
must the intensest heat be generated by the impact of two 
nebulous masses, one, or both of which together, may em- 
brace more matter than all our planets and the sun com- 
bined — as much even as the matter of our entire visible 
firmament of stars.* One experiences a distinct feeling 
of relief in the discovery of such a possible means of igni- 
tion of nebulae. Our first discovery of nebulas disclosed 
them existing already at an intense temperature. Again 
and again the question has been raised, " Whence the 
heat?" We could only reply, "That is a mystery. The 
incandescent condition may be primordial. Who knows 
but matter may be created incandescent ? " Such answers 
and such suggestions have been offered. Now, in accord- 
ance with the theory of nebular conglomeration, we may, 
if we please, recognize the 2)0ssibilUi/ of the creation — or 
at least, the normal existence — of matter in any assigna- 
ble state; but we have grounds for tracing nebular history 
one step farther back. We must conceive of dark nebulae 
that have not yet been pounded into a white heat. We 
must conceive of nebulous particles now first marshalling 
raw recruits of matter into a forming phalanx. Even yet, 
the mystery of beginnings hangs over us. We have not 

* These sentences were written before the arrival of Natur-e of January 10, 
1878, where a communication of James Croll sets forth an identical suggestion. 
On the heat generated by the impact of cosmical bodies see also Croll : Climate 
and Time, p. 353. Two bodies each half the mass of the sun moving directly 
toward each other with the velocity of 476 miles a second, would by their con- 
cussion generate in a single moment heat sufficient to last 50,000,000 years at the 
present rate of solar radiation. 



94 XEBULAR LIFE. 

yet seen molecules rolling themselves up into visibility. 
We have never, even in imagination, seen atoms emerging 
from the dread abyss of nothingness. Let us explain all 
we may; let us seek out all antecedent conditions possi- 
ble, enough will still remain to pique our curiosity, and 
awe us by its mystery. Nay, the farther we trace the 
links of the chain of causation, the more palpably we feel 
the need of some support which is not one of the links in 
the chain, but is superior to the principle of finite causa- 
tion, and is self-sufficient, existing out of relation to suc- 
cession, time and space. 

§2. XEBULAR ROTATION. 

1. Causes of Rotation. — It thus appears that the 
hypothesis of nebular conglomeration explains two other- 
wise inexplicable phenomena — nebular amorphism and 
nebular heat. A third phenomenon, hitherto m^'sterious 
and unexplained, is equally accounted for. That is, the 
rotary motion which sometimes arises in nebulous masses. 
This difficulty has often balked belief in the nebular theory 
of the origin of the solar system.* The moment, however, 
that we recognize the probability of the collision of nebu- 
lar masses, the idea of rotation necessarily arises. A 
nebular mass comparatively minute, impinging upon a 
mass of any dimensions, would inevitably generate a rota- 
tion, in every case except when the centres of gravity of 
the two masses moved toward the same point, and (unless 
moving in the same staight line) with such velocities as to 
reach it at the same instant. This is a case which is im- 

*Rev. W.B. Slaughter saj's: "It is to be regretted that the advocates of 
this [nebular] theorj' have not entered more largely into the discussion of it 
[the origin of rotarj' motion]. No one condescends to give us the rationale of it. 
How does the process of cooling and contracting the mass impart to it a rotary 
motion?" (^The Modern Genenis. p. 48.) Even Helmholtz says the rotation 
"must be assumed."' (Interaction of Natural Forces, Youman's ed., 231; 
Popular Scientific Lectures, 115.) 



NEBULAR ROTATION". 



95 



possible in the ratio of millions to one. I have heretofore 
stated that when the two bodies consist of matter as dense 
as the earth and a cold meteorite descending from a distance 
of a hundred thousand miles, the small body would proba- 
bly be so much deflected by lateral attractions as to miss 
the large one, and would, consequently, begin to revolve 
about it in an orbit more or less elliptical. With masses 
of matter as voluminous as nebulae, such orbital revolu- 
tions must sometimes be established ; but it is very appar- 
ent that the collision is vastly more probable than in the 
case of smaller and denser masses. Motation, conse- 
quently, would be the gevieral condition of 
nebular masses. 

Now, let us consider the two general 
cases which would arise in the impact of 
nebula against nebula. 

(1.) First Case. — The centres of gravi- 
ty of two nebulm move toward one point 
with such velocities as to reach it simul- 
taneously. We recognize at least two 
sub-cases. 

(a) When the centres of gravity move 
along one straight line. Here in the pos- 
sible case in which no rotation would 
ensue, the resultant nebula, in addition to 
a distorted form, would simply experience 
an altered motion of translation in space. 
If three nebulae. A, B and C, (Figure 19) 
lie with their centres of gravity in one 
straight line, each centre of gravity is 
drawn toward each "of the others with a 

force proportional to the masses and the 

^ /. , T Figure 19. Mo- 

mverse squares ol the distances. At the tion of Three 

end of a certain time, B would be drawn by N e b u l .*: in 
the attraction of A to b, and by the attrac- sub'-case T.^ 




96 



XEBULAR LIFE. 



tion of C, to ^'. C would be drawn by the attraction of 
A to c, and by the attraction of B to c'. A would be 
drawn by the attraction of B to a, and by the attraction 
of C to (7o ; its resultant place would be, therefore, at a' . 
The new positions are therefore b' , c' and a' . A has 
made some movement toward B, but C has made more in 
the same direction. C is therefore approaching A, and 
will eventually join A, and coalesce with it. The virtual 
motion of A in the direction of C will therefore cease, 
and A will move toward B with a velocity increased by 
the amount by which C's former attraction drew A toward 
C. That is, the translation of A through space will be 
augmented by the impact. 

{b) The second sub-case is when the centres of gravity 
do not move along one straight line. Here A (Figure 20) 

is attracted b}^ B and C, 
and the resultant of the 
two attractions brings A 
to a. Similarly, B is at- 
tracted b}^ A and C, and 
takes a course between 
the two attractions to a. 
Finally, C is attracted by 
A and B, and arrives at 
a at the same instant 
when, by hypothesis, A 
and B arrive at the same 
point. It is evident that there will be ilo tangential re- 
sultant, and no rotation will ensue; but the united mass 
will undergo a translation in space, in the direction of the 
resultant of three momenta. 

(2.) Second Case. — The centres of gravity move toward 
a coinmon point icith such velocities as to ^:>«ss it succes- 
sively. The nebula A is attracted by B and by C (Fig. 
21. The last figure also illustrates this case, supposing 




Figure 20. ^[otiox of Three Xebvl^ 
IN Space. Case I, Sub-case b. 



NEBULAR ROTATTOK". 



97 



the three bodies to reach a successively). B is also at- 
tracted by C, but owing to relative positions and masses 
(as we may assume) is less affected by C than A is. A 
and B both move toward a, but A will reach the point, let 
us suppose, a little before B. It will be struck by B 
therefore, tangentially, and both nebulous masses, at least 
upon their exterior, will acquire a rotation in the same 
direction. If the 
deflecting force ex- 
erted by C is such 
that A and B ap- 
proach each other 
to a distance but 
little less than the 
sum of their radii, 
they will not co- 
alesce unless their 
velocities are low, 
but will each ac- 
quire a rotary mo- 
tion, and each pass 
on maintaining a 
separate existence. 
But if their cen- 
tres of gravity ap- 
proach within a 
distance sufficient- 
ly less, than the sum of their radii, the two nebulae will 
coalesce. Until completely coalesced, they will present 
the form of a dumb-bell, and afterward, of an irregular 
spiral, whose irregularity will continually diminish as 
the coalescence proceeds. In this way, forms like H 
1,173 and H 1,622 (Fig. 8) would be evolved. 

It is quite conceivable that nebular rotation might be 
generated by attraction, in cases where no actual impact 
7 




Pig 21. Motion of Three Nebul.b in Space. 
Case II. 



98 



NEBULAR LIFE. 



takes place. Suppose an amorphous nebula A (Fig. 22) to 
be so situated in respect to B, that its longer diameter 
a h, makes an oblique angle with the line A B, joining the 
centres of gravity of the two nebulae. One extremity of 
the mass, as at b^ will experience a greater relative attrac- 
tion toward B than the other extremity of the mass will 

experience; and this 
inequality will con- 
tinue as long as the 
angle B A 6 is not a 
right angle, and, in 
the case supposed, as 
long as B A ^ is less 
than a right angle. 
The effect must be to 
turn the nebula A in 
such direction that its 
longer diameter pro- 
duced will tend to 
pass through the cen- 
tre of gravity of B. 
But in the meantime, 
B and A may have 
travelled to widely 
separated regions of 
space. The rotation 
begun in A will there- 
fore Continue unhin- 
dered. It will continue in any case where the hindering 
action of B is less than the action which inaugurated the 
rotation; as for instance when the form of A becomes 
more svmmetrical, though the action of B should be 
reversed by change of position, without being less.* 




Fig 22. Rotation Resulting Without 
Actual Impact. 



* A modern writer of much sagacity has maintained that an amorphous 
nebula would be made to rotate by the tangential action of currents of nebulous 



N^EBULAR ROTATION". 09 

2. Causes of JVehdar Forms. — As to the spiral form 
of nebulae different sug-gestions may be made. We may, 
for instance, conceive it as arising from the action of a 
resisting medium in space. This would develop a retarda- 
tion in the peripheral portions, and would explain the 
tendency of parts to be left behind, as indicated in certain 
features of spiral nebulse. Other phenomena would be 
explained on the suppc-sition of some translation through 
a resisting medium. The unequal actions resulting from 
a non-homogeneous constitution of the nebula would favor 
the production of a spiral form. 

Professor Daniel Kirkwood has offered the following 
suggestion on this subject: "The tendency in a rotating 
nebula, to unequal angular velocities, resulting from the 
increased rapidity of condensation from the equator to- 
ward the centre, may perhaps also account for the phenom- 
ena of spiral nebulae. If, in a contracting mass of vapor, 
a free motion of the particles among themselves be 
established before the centrifugal force becomes equal to 
the centripetal, a spiral convergence like that of 51 in 
Messier's Catalogue would naturally ensue."* As the 
motion among the particles can never be perfectly '' free," 
it is questionable whether the result would not be a strati- 
fied nebula, rather than a spiral one. The only probable 
cause of a descent of particles toward the centre would be 
their superior inherent density. These, carrying with 
them the higher linear velocity of the exterior, would tend 
to run ahead of the particles whose original position was 

matter descending from higher to lower levels simply by the action of the central 
gravity of the mass (Jacob Ennis: The Origin of the Stars, 221 seq.). It is, how- 
ever, a fundamental principle in physics that no rotation could be generated in 
such a mass by the action of its own parts. As well attempt to change the 
course of a steamer by pulling at the deck-railing. The same author suggests, 
however, that the attraction of neighboring nobulte would contribute to the 
formation of surface currents; and he even suggests the origination of rotary 
movements by nebular impact. 

* D. Kirkwood, Amer. Jour. Sci., II, xxxix, G8, Jan. 1865. 



100 NEBULAR LIFE. 

less exterior. Now friction would tend to equalize these 
motions, but as we may admit that this result would not 
be accomplished instantly at each stage of their progress, 
we must conceive a spiral motion of such particles. But 
there seems to be no probability that the relative number 
of such particles would be so great as to impart a con- 
spicuous spiral structure to the whole central mass. And 
if it should, to what could it amount? The motion is from 
all sides spirally toward the centre; the possible amount of 
it is therefore limited. The permanent condition of the 
interior would be either rotation in annuli or rotation with 
the same angular velocity as the exterior. Evidently, the 
progressive acceleration of motion in these nebulae must 
be from the centre, not toward it — unless the form results 
from retardation peripherally, as I have suggested. 

As to the general internal mass, aside from the descent 
of particles, as supposed, it rotates with the same angular 
velocity as the exterior, and in the progress of contraction 
it undergoes acceleration in the same proportion as the 
exterior. I think the case may be pushed further. The 
process of contraction would shorten the radius of revolu- 
tion of exterior particles a greater amount than the radius 
of interior particles; and hence the external parts would 
be more accelerated than the internal; and the internal 
would rotate with less, instead of greater relative angular 
velocity.* It is true that a given amount of radius- 
shortening in the exterior parts would cause less accelera- 
tion of angular velocity than the same amount of short- 
ening in the internal parts, since the angular velocity 
varies inversely as the square of the radius; but in a 
regular process of shrinkage the radius of revolution of 
the external particles would be shortened by an amount 
equal to the sum of the shortenings of the radii of all the 
particles within it; and this would give the external 

* Sec, further, Part II, ch. i, §2, 2, (2). 



I^EBULAR ROTATIOI^. 101 

particles a much greater acceleration than the internal. 
Though this is not the nature of Professor Kirkwood's 
reasoning, we may inquire whether excess of angular 
velocity in the external parts would not develop a spiral 
structure. Of course, that would be the tendency, and 
the motion would not reach a limit, as in the case of 
internal particles moving spirally toward the centre. The 
spiral structure, however, would be reversed. But all this 
peripheral excess of motion would be opposed by mutual 
friction of parts and by the resisting medium. Nor is it 
conceivable that the slight residual excess of peripheral 
motion should develop so strong a tendency to diverge 
tangentially from the general centre of gravity as is mani- 
fest in actual spiral nebulae. The spiral structure would 
be close and entirely inconspicuous. 

Professor G. A. Hinrichs thinks the spiral form must 
result, in a large nebula of greatly excessive internal den- 
sity, from the excessive rotary velocity of the interior 
portions.* This conception is perhaps not distinct from 
the last; and the same comments may be made upon it. 
Furthermore, it implies — what may not generally be 
true — that the central density was acquired after rotation 
began; and it must be confessed that rotation is likely 
to be an early incident of nebular life, and much aggrega- 
tion of matter is likely to follow. But it may be further 
said that this central acceleration, should it become a fact, 
would seem to be a process most likely to arise in an 
advanced stage of the nebula, when the symmetry of out- 
line would not, by the mere reaction of internal rotation, 
develop those patchy forms which characterize many of 
the spiral nebulae. The spiral form is primitive. It is not 
a form of equilibrium; it tends to settle into the oblate 
spheroid; and this is the form to be expected after nebu- 
lar life has advanced far enough to develop, if it were 

* G. A. Hinrichs, Amer. Jour. Science^ II, xxxiz, 141-3. 



102 KEBULAR LIFE. 

physically possible, any excessive internal rotation. Fi- 
nally, any spiral arrangement resulting from excess of 
internal rotation would be closely coiled, approximating a 
spheroid, and not by any means the enormous open coils 
of the actual nebulae of this class. 

Mr. Herbert Spencer has conceived that a multitude of 
flocculent nebular masses descending from the outer por- 
tions of an extensive nebula, would be arranged in a spiral 
manner;* and an anonymous writer has expressed the 
opinion that the simple process of contraction in a diffused 
nebulous mass, or spiral descent of its constituent parts, 
would develop a spiral form.f 

A nebula shaped like a sickle presents the appearance 
of a nebulous body moving in an orbit through a resisting 
medium. The resisting medium is probably a fact. The 
orbital motion would be attributable to two forces — one 
an impulse exerted tangentially, and the other a constant 
force exerted centrally. The tangential force it is not 
difficult to conceive as existing. A central force, indeed, 
is exerted by every cosmical mass of matter; but a central 
force ruling the orbital movement of an external body 
must contain a large mass relatively to the moving body. 
The central body should, therefore, be as visible as the 
body moving around it.'l Now when we contemplate the 
sickle-shaped nebula H. 3,239 (Figure 7), we detect evi- 
dences of the orbital motion of a body, but do not dis- 
cover the body which could serve as its centre of motion. 
We might conjecture that such body has not yet become 
luminous; but even then, the orbit of the revolving body 
is so small relatively to its volume, that we can hardly 
suppose a body of sufficient mass could be contained 

* Spencer, Westminster Revieiv, Ixx, 114, July, 1858. 

\North Ajnerican Review, xcix, 26, July, 1864. 

tin any case, it will be remembered, whatever the relative sizes of the two 
bodies, each really revolves around the common centre of gravity between 
them. 



NEBULAR ROTATTON. 



103 



within it. The con- 
ception of an orbital 
motion as the cause 
of the sickle form pre- 
sents difficulties which 
we must try to escape 
by some different sup- 
position. 

Let us assume a 
considerable mass mov- 
ing in the direction 
from B to C, Figure 
23. A nebulous mass 
located at A, would 
be drawn at first in 
the direction A B. If 
it moved in a resisting 
medium it would be- 
come somewhat elon- 
gated in that direction 
— the lightest parti- 
cles being kept behind. 
When the attracting 
body had reached «', 
the nebula would be 
drawn toward that 
point — its direction 
beingslightly changed. 
So, as the attracting 
body reached the points 
f<2j «3j «4j «5> «6» <^7 and 
C, the nebula would 
be drawn successively 

Fig, 23, Possible Origin of 

THE Falcate Form 

OF Nebula, 




104 KEBULAR LIFE. 

toward those points. That is, it would move in a curve 
with a radius continually diminishing, as long as the at- 
tracting body should continue to approach; but with a 
radius gradually increasing again, after the attracting 
body should begin to recede. In other words, the path of 
the nebula would be a curve with two branches somewhat 
symmetrical with respect to each other. 

It ought perhaps to be said that the attracting body 
feeling the reciprocal influence of the nebula, would not 
move along t\\^ straight line B C, but along the hyperbola 
B' D E. 

The gyratory motion of a nebula which is not homo- 
geneous would result, in a resisting medium, as I have 
already indicated, in a spiral form. But, if the nebula 
should slowly assume a homogeneous character, having 
similar density throughout each concentric zone, the spiral 
would be gradually succeeded by a rotating spheroid. A 
nebulous mass homogeneous from the beginning, and sym- 
metrical in form, would probably never assume the form of 
a spiral. One appointed form then, of all rotating nebulae, 
is that of a spheroid. 

3. Influence of Resisting Mediinn. — One suggestion 
which may be of importance in a subsequent discussion, 
remains to be made. If a resisting medium act on the 
motions of nebulous masses in space, it would not onl}'- 
induce a spiral form in a non-homogeneous rotating nebula, 
but in a homogeneous one would slowly establish a rela- 
tive retrograde movement of the superficial portions. 
This, by friction with the deeper portions, would tend to 
retard their rotary motion, and thus, as a final consequence, 
the total rotary motion would be retarded. The actual 
velocity of rotation would never be, therefore, in a nebula 
continuing to condense after rotation had begun, as rapid 
as would be demanded by the shortened radius of the ro- 
tating spheroid. It may be further said that the estab- 
lishment of a retarding superficial current would not 



NEBULAR ROTATION. 105 

necessarily be restricted to nebulae of uniform density. 
Whenever the nebulous matter should have become some- 
what closely and uniformly gathered together within a 
certain space, the included portions of the resisting medium 
would partake of the gyratory motion of the nebula, and 
the superior power of a denser interior to overcome ethereal 
resistance would have no opportunity to exert itself. 
Hence a gradually increasing internal density would not 
affect the formation of retarding superficial currents in a 
nebula in this sense non-homogeneous. 

Whether rotating or stationary, every nebula is con- 
tinually wasting its heat. The process of refrigeration is 
probably retarded by the frequent impact of new accessions 
of matter. Inevitably, however, the nebula must, in the 
progress of ages, become reduced in temperature. 

4. Nebular Evolution icithout Rotation. — In a non- 
rotating nebula, especially if 
possessing an irregular and ex- 
tremely flattened shape, we may 
contemplate, besides the general 
centre of gravity, the centres of 
gravity of its different portions. 
Under certain conditions in the 
course of cooling and shrinkage, 
a nebula may break up into y\q. 24. 

numerous pieces by a process Coagulating Nebula, or 

, ^ , . , "Curdling Fire-mist." 

analogous to a coagulation and 

withdrawal of part from part (Figure 24), as is daily illus- 
trated in the patchy arrangement of the aqueous vapors 
which float in our atmosphere.* Under other condi- 

* Of a certain porlion of the nebula in Orion, the so-called Huygcnian region, 
Sir John Herschel writes as follows: "I know not how to describe it better than 
by comparing it to a curdling liquid, or a surface strewed over with flocks of 
wool, or to the breaking up of a 'mackercT eky when the clouds of which it 
consists begin to assume a cirrous appearance. It is not very unlike the mot- 
tling of the sun's disk, only (if I may so express myself) the grain is much 




106 NEBULAR LIFE. 

tions, as we may reasonably suppose, liquefied molecules 
may gather about numerous partial centres of gravity 

(Figure 25), as was first sug- 
gested by Sir William Her- 
schel. In either case, as the 
cooling should proceed, a 
cluster of luminous bodies 
would come into existence, 
which would present the ap- 
pearance of a resolvable 
nebula. This is, perhaps, a 

Fig. 25.— Fokmatiox of Local -, ^ i , • n 

^, . ^^ . mode ot evolution of non- 

rotatino- nebulae. 




Nuclei in a Nebula. 



§ 3. XEBULAR AXXULATIOX. 

1. The Load of Equal Areas. — It is probable that 
most of the nebulae have rotary motions. It would seem 
that mutual attractions, if not actual collisions, must, in 
the great majority of cases, generate rotations in one or 
another of the methods already indicated. In fact, when 
we contemplate the delicacy of the adjustment of the 
forces acting on a tenuous body poised in distant space, 
and surrounded by millions of other bodies, all changing 
perpetually their relative distances and positions, it be- 
comes almost incredible that a resultant should not arise, 
in the course of millions of years, which should act, how- 
ever faintly, as a tangential force. Once stirred from 
a rigid attitude, a motion is initiated which must change 
fundamentally the course of nebular development. Let 
us consider the course of development which the laws 
of physics necessitate, when a rotation has been inau- 

coarser and the intervals darker: and the flocculi, instead of heing generally 
round, are drawn into little wisps. They present, however, no appearance of 
being composed of small stars, and their aspect is altogether different from re- 
eolvable nebulce.'" {Memoirs of (he Astronomical Society of London, vol. ii.) 



NEBULAR ANNULATIOK. 107 

gurated in a mass of highly heated vapor suspended in 
space. 

No proof is required that such a heated body would 
radiate its heat into surrounding colder space. No proof 
is required that it would coincidently contract. To sup- 
pose otherwise would be to assume an order of nature 
different from that which all induction has established; 
and this would bring to a summary end all reasoning on 
physical subjects. But a shrinkage in the volume of a 
rotating nebula would necessitate an acceleration of its 
rotation. By a mathematical principle of physics, known 
as "the law of equal areas in equal times," the sum of 
the products of the particles of a rotating vapor into the 
areas described by their radii vectores projected on the 
plane of the equator, is always, in the same body, a con- 
stant quantity. In other words, each radius vector 
describes the same area, whether its length be increased 
or diminished; and hence, if its length is diminished its 
angular velocity must be increased to enable it to sweep 
over the same area in the same time. This principle, thus 
enunciated, may not be quite clear to some of my readers, 
and I will endeavor at least to render intelligible the 
meaning of the proposition, though its proof could not be 
presented without resort to mathematical operations. 

Let us suppose that in Figure 2G the circle ABC 
represents a section through a rotating sphere of heated 
vapor, in the plane of its equator. The circumference 
ABC is, therefore, the equator, and it may be conceived 
as represented by a series of particles linearly arranged. 
Let one of these particles be at a, then a O, drawn from 
it to the centre of the circle, is its radius vector. If, in 
the progress of rotation, the particle a is transported to 
6, its radius vector will sweep over the space between O a 
and O h. But suppose that in the course of time, cooling 
has contracted the sphere to such extent that when the 



108 



NEBULAR LIFE. 




Fgi. 26. The " Law of Equal Areas,"' 



same molecule ar- 
rives in the same 
angular position as 
before, it is not at 
«, but at a . Its 
radius vector is now 
O a', a certain 
amount shorter than 
before, and if it 
sweeps forward with 
the same velocity as 
before, it will not 
sweep over the same 
area in the same 
time as before. It 
must, therefore, move more rapidly, so that in the same 
time which formerly carried it from a to b, it will now be 
carried from a' to b' , making the area a'O b' equal to the 
area a O b. If these statements are true of one particle 
in the circumference of A B C, they must be true of all the 
particles in that circumference. But immediately within 
this circumference we may conceive another, the particles 
of which are moved in every respect exactly like those in 
the circumference ABC, except that their absolute veloc- 
ity is less all the time. As the sphere contracts, these par- 
ticles also will move with accelerated velocity. But within 
the last named circumference we may conceive others, 
until the whole area inclosed within A B C is seen made 
up of a series of concentric circles of particles, each par- 
ticle rotating according to the same law as the particle 
at a. Next, we may easily conceive that another sheet of 
particles is immediately contiguous to this one on each 
side. The motions of its particles, it will readily be under- 
stood, are controlled by the same law of equal areas. It 
follows that the rotation of the whole sphere, which is 



liTEBULAR ANNULATTON". 109 

made up of parallel sheets of particles, must be accelerated 
ill the same manner as the particle at (f, during a process 
of cooling and contraction of the mass.* 

The same conclusion may be reached from the principle 
that the angular velocities of two rotating spheroids hav- 
ing the same mass and the same angular momentum, but 
of different equatorial diameters, are to each other inversely 
as the squares of their radii of gyration. f The radius 
of gyration is the distance from the axis of rotation to 
the centre of gyration, or point within the mass at which 
we can conceive an opposing force applied which would 
completely arrest the rotation without jarring or wrench- 
ing the axis. 

Not only is the angular velocity increased, but the 
actual velocity of the periphery also; and it is chiefly the 
increase of the actual velocity which increases the cen- 
trifugal force of a particle. Some critics fall under the 
misapprehension of considering only angular velocity. t 
That contraction increases the actual as well as the angular 
velocity is obvious from the simple consideration that the 
centrifugal force of a particle at the equator is measured 
by the square of the actual velocity divided by the radius 

*In this explanation, the particles, for the sake of simplicity, are assumed 
to be ail of the same mass. Thus under the principles enunciated, they become 
a common factor which may be cancelled. 

t The angular momentum of a spheroid whose mass is M, axis of gyration, k, 
and angular velocity, 9, is 

Supposing the same mass to have contracted till its axis of gyration ]s k' 
and the angular velocity 6', its angular momentum will be expressed by 

But as the angular momentum remains constant, we have 
Mk-^9 = Mk'^e\ 
whence -. 6' :: k'^ : k'^. 

And for a particle iu the periphery, k and k' equal the radii vectores r and r' 
In the two positions, and we get 

0:0':: r'« : r^. 
That is, the angular velocity increases as the square of the radius vector of 
the particle diminishes. 

$Rev. W. B. Slaughter: The Modern Genesis, pp. 85-87. 



110 KEBULAR LIFE. 

of the equator. Since, therefore, the radius is continually 
diminishing, the actual velocity is continually increasing.* 
2. Abandonment of a Ring. — Let it be granted then, 
that the process of necessary cooling and contraction 
would be accompanied by an accelerated rotation. This 
would be accompanied, in turn, by an increased oblateness 
at the extremities of the axis. As soon as rotation begins, 
the momentum of the particles around the equator is 
greater than that of particles on either side, and it con- 
tinually decreases to the poles, where it is nothing. The 
momentum of a particle measures its tendency to fly off 
in a tangent or straight line in the direction in which the 
particle is moving at any instant. This is a tendency 
which, in part, draws it away from the axis around which 
it moves. As the velocity of rotation increases, each par- 
ticle must therefore experience a stronger tendency away 
from the axis of rotation. As this centrifugal tendency 
is greatest at the equator, the equatorial parts will pro- 
trude, and, if there is any mutual attraction among the 
particles, those on each side of the equator, aided by cen- 
trifugal tendency, will flow away from the poles, and thus 
diminish the polar diameter, while the equatorial is in- 
creased. In other words, the sphere will become an oblate 
spheroid, with oblateness increasing in proportion as the 
velocity of rotation is increased. 

What must this process end in? Evidently, the ob- 
lateness will finally reach such an extent that the equa- 

* Letting v and v' represent the actual velocities of a particle, w, in the two 
situations, before and after a certain amount of contraction, and r and r' the 
two corresponding values of the radius vector, the centrifugal force in the two 

situations will be and . But as the centrifiieal force varies directly 

?• r' 

as the centripetal force, that is, inversely as the square of the radius vector, we 

have 

r r' 

From which r^ : t''2 :: r' : r. 

But ^ > T\ .'. V^ > r2 or v' > v. 



NEBULAR AKNULATION'. Ill 

torial particles will have a centrifugal tendency equal to 
the centripetal. Then, if any further contraction of the 
spheroid takes place, the equatorial particles will not fol- 
low, but will be left suspended in equilibrium between the 
two tendencies. An entire equatorial ringlet of particles 
will attain tliis equipoised condition, and the remainder of 
the mass will proceed to shrink away from it. (See Fig- 
ure 27.) 

3. Width of t/ie Ring. — Now, if we could neglect 
the mutual attractions of contiguous particles, it is ap- 
parent that this ringlet would be extremely narrow and 
tliin. As soon as detached another slender ringlet would 
separate itself, and then immediately another, and so on. 
The series of slender concentric ringlets thus detached 
would constitute virtually a broad, flat and thin ring, hav- 
ing a slower rate of rotation on its outer margin than on 
its inner. If these closely contiguous ringlets should 
actually coalesce, the friction of outer and inner ones 
would accelerate the outer and retard the inner until the 
angular velocity of all would approach uniformity. But, 
disregarding mutual attraction of the parts, we see no 
cause to limit the process by which slender ringlets would 
be formed, until the whole mass of the spheroid should be 
reduced to a rotating disc essentially continuous from cen- 
tre to circumference. But here two suggestions must be 
made. The discoid arrangement would be but a momen- 
tary phase in each concentric ringlet, because (1), when 
we carry the conception to the extent indicated, we per- 
ceive that disc-like continuity from ringlet to ringlet is in- 
compatible with the physical tendency to ever increasing- 
velocity toward the centre in proportion as the contraction 
is actually experienced toward the centre. (2) Such a 
disc could not subsist in the case of a fluid substance. It 
would gather itself into a sino-le ring-. The transverse 
section of the ring would be ovate, with the smaller end 



112 KEBULAR LIFE. 

turned toward the axis of rotation. Whatever we might 
conceive to result from unequal velocities in a flat ring of 
relatively limited extent, it is evident that no permanent 
disc-like continuity of successively equilibrated matter 
could ever take place to any relatively considerable extent. 
Instead of a broad and continuous disc, we must have a 
series of concentric rings rotating with different velocities. 
Nor is it supposable that closely approximated ringlets, 
circumstanced as suggested, would perpetuate their com- 
mon existence until some epoch when a common crisis 
should simultaneously change the condition of newer and 
older alike.* 

Undoubtedly, mutual attractions of contiguous parti- 
cles and masses always existed, and hence we have no 
occasion to speculate on the consequences of an absence 
of such attractions. If then, we turn back in thought to 
the epoch when the first equatorial ringlet of particles 
should have been left detached from the shrinking re- 
mainder, we perceive that the next inner circle of particles 
must be actuated by a centripetal force barely sufficient to 
overcome the centrifugal tendency experienced in that 
circle. But exterior to these particles is the ringlet of 
particles just disengaged, and its attraction would com- 
pletely neutralize the slight excess of centripetal force 
experienced by the second ringlet, and this ringlet would 
therefore be brought into a state of equilibrium, and 
would also be left. Now the third ringlet would experi- 
ence a stronger predominance of centripetal force, but 
this would be opposed by an increased attraction exerted 
by the two ringlets exterior to it. We may therefore 
conceiv^e that a third, and other ringlets would almost 
simultaneously become detached. How broad and massive 

* It has been suggested that such a history is supposable. See D. Kirk- 
wood, Amer.Jour. Sci. II, xxxviii, 5; D. Trowbridge, irf. note; S. Newcomb: 
Popular Astronojny, 497-8; Du Prel: Die Plcmetenbewohner, 6. 



NEBULAR ANNULATIOX. 113 

the aggregate ring would be, would be determined by the 
position of the nascent ringlet at which the centripetal 
force should exceed the centrifugal force (at that distance 
from the axis) added to the attraction of the annular mass 
exterior to it. Now every successive addition which may 
have been drawn to the annular mass increases its distance 
from the next ringlet of particles, and upon this its influ- 
ence, though increasing with the growth of the ring, 
diminishes as the square of the distance increases. Its 
influence, that is its contribution to the centrifugal ten- 
dency of the next ringlet, diminishes, therefore, more 
rapidly than the centripetal tendency is diminished by dim- 
inution of the residual mass, for that is as the first power 
of the mass; and it increases as the square of the radius of 
the spheroid is diminished by contraction. The influence 
of the ring diminishes more rapidly than the joint effect 
of diminished residual mass and increased rate of rotation. 
This circle of equilibrium would determine, therefore, the 
line of separation between a segregating annular mass 
and the residuum of the spheroid. In other words, 
an annular mass of relatwely considerable amount 
vioiild separate^ and a secidar interval VDOidd intervene 
before the separation of another annidar mass.^ The 
condition represented by Figure 27 may therefore be 
contemplated as one of the primitive 
phases of a rotating nebula. It is 
observed to actually exist in certain 
stellar nebulae, as H 450. 

The foregoing exposition assumes 
that the actions concerned would 
reach their resultant somewhat sim- 
ultaneously, and the rino- would be 

» 1 • 1 -111 Fig. 27. Nebula in Pko 

tormed without any considerably cess or Annulation. 

* Compare D. Trowbridge, Amer. Jour. Sci., 11., xxxviii, 35. 
8 




114 



l^EBULAR LIFE. 



prolonged period of growth. The influence of progressive 
contraction of the nebula is therefore neglected. But 
contraction would proceed during whatever period might 
be occupied in the formation of the ring. We may con- 
sider, therefore, what would result on the assumption that 
no ringlet, after the first, would leave the nebula until 
entirely equilibrated between centripetal and centrifugal 
tendencies. This assumption depends on progressive con- 
traction and acceleration for the successive disengage- 
ment of ringlets. It will give a clearer conception of the 




Fig. 28, Illustrating the Determination of the Width of a Nebulous 

Ring. 



conditions limiting and determining the width of the ring 
produced. Let a h (Figure 28) represent a segment of a 
slender ringlet just abandoned, having the slight interval 
a k, separating it from the new periphery of the nebula. 
Soon the peripheral ringlet k I will attain a state of equi- 
librium. This experiencing a positive attraction from the 
ringlet a b, and no tendency to fall toward the centre of 
the nebular mass, must move toward a h. The external 
ringlet becomes thus augmented to the breadth shown 



NEBULAR AJ^NULATION". 115 

in be, and the interval between it and the nebula is en- 
larged to c/ in. Next, another ringlet in n attains a state 
of equilibrium, and will similarly be drawn to h c, augment- 
ing the external ring to the breadth c i shown in c d. In 
due time tlie ringlet o^:> is abandoned and drawn to c d, 
augmenting it to the width dii as shown at d e. I do not 
conceive the actual formation of distinct ringlets of any de- 
finable magnitude, with an actually periodic passage from 
the periphery of the nebula to the growing ring. The 
abandonment of ringlets is momentary and continuous, and 
the passage of the nebulous matter outward is in the nature 
of a continuous flow which fills the intervening space with 
an extremely attenuated nebulous medium. 

At length the breadth of the growing ring becomes 
such as is represented at ef, and the interval between it 
and the nebula has widened to w s. Meantime the attrac- 
tion of the ring exerted upon the periphery of the nebula 
has been continually diminishing as the square of the 
distance increased. It has become diminished to such an 
extent as to be comparatively feeble. A differential ring 
st, feels now a different preponderance of forces. The 
attraction of the ring does not cease to be felt to some 
extent; and the attraction of the nebula does not cease to 
be neutralized by the centrifugal tendency. But there 
have all along been two actions opposing the passage of 
matter to the ring which have not yet been mentioned. 
One of these is the friction of the ether and meteoroidal 
matter, which continually retards the velocity of rotation, 
and all the more where a mass as thin as the withdrawing 
ringlet is concerned. This diminishes the centrifugal ten- 
dency, and opposes the passage outwards. Besides this, 
the mutual attraction of contiguous parts of the ringlet 
at all times opposes that distension implied in the trans- 
formation to a ringlet of greater circumference. The joint 
action of these comparatively minute forces determines 



116 XEBULAR LIFE. 

a critical moment. The diminished attraction of the ring 
now ceases to overcome them. A ringlet is formed at st 
wiiich remains unmoved from its place. It constitutes the 
starting point of another ring, which, in turn, goes through 
a similar history.* 

Under certain conditions the STOwth of the ring- would 
not attain its limit until the nebula had been entirely ex- 
hausted. The nebula would be thus transformed into an 
annulus. If the resistances of friction and the mutual 
attraction of parts of the ringlets should in any case be 
inconsiderable, the attraction of the ring would always 
preponderate over the forces opposed to the translation of 
matter to it, and the growth of the ring would be indefi- 
nite, f 

It does not seem unreasonable to suppose that under 
certain conditions, as for instance, an extraordinarily rare- 
fied condition of the central part, the centrifugal tendency 
of the peripheral parts and the attraction of the nascent 
ring for successively more interior nascent rings should 
result in expanding the entire mass of the nebula directly 
into an annulus. This tendency once inaugurated, by the 

* Let G' = attraction of the ring upon the nearest point of the nebula, i.e. 
sum of the components (of all the attractions of the ring) which act along the 
shortest line from the point to the ring. 

G = atttraction of nebula upon the same point. 

F = centrifugal tendency of the same. 
e = sum of frictional resistances to its motion. 

m = sum of mulual attractions opposing separation of particles. 

Then, as long as we have 

G' + F>G + e + m 
the ring will continue to increase in breadth. When 

G^ + F = G + e + m 
the ring will cease to receive accessions of new ringlets. Thenceforward we 
shall alwaj's have 

G' + F < G + e + m. 

t Since, in this case, e -\- 7n = 0, and by hypothesis G =F at all times when 
annulation is possible, the expression G'-fF> G -\- e -\- m reduces to G' > 0, 
an inequation which expresses the condition of ring-growth, and will continue 
true until e -f- m becomes such that G'= e -\- m. But if the last relation is never 
reached, the growth of the ring will be unlimited as long as the nebula is unex- 
hausted. 



KEBULAR ANl!TULATIO]N". 117 

vacation of the central region, the effect of further con- 
traction would be, in a highly tenuous condition of the 
nebula, to enlarge the diameter of the vacant interior, as 
well as to diminish the outside diameter of the ring. 

A tendency of this kind to the simple annulus is by no 
means imaginary. The central attraction of parts near 
the centre would, on physical principles, be slight, since 
nearly as much matter would lie upon the side toward the 
periphery, />, Figure 29, as on the side toward the centre, 
c. At the centre the balance of tendencies would be com- 
plete. The periphery and the centre 
would therefore be, by hypothesis, 
both in equilibrium. The periphery 
would experience no tendency to 
move toward the centre. The cen- 
tral portions would experience little 
or no tendency to remain there. 
Meantime both parts attract each 

,1 rpi • 1 'xu JFiG- 29. Nebula, Becom- 

other. The periphery, with progres- ^^^ annular. 

sive shrinkage, might move toward 

the centre until accelerated velocity should nullify the 
attraction of the central portion. The latter portion 
would move, by its own gravity, toward the periphery, 
until a state of condensation should be reached, such as 
to correspond with the existing temperature. Thus, I 
imagine, a simple annular nebula might originate, such as 
we are acquainted with in the Lyre (Figure 11), in H 
1,909. and H 2,621. 

Thus, nebular aggregation and secular refrigeration 
may reasonably be regarded as the general causes of the 
varied forms, conditions and evolutions of nebulne. Let 
us now attempt to trace the development some steps 
farther. 

*Schellen: Spectral Analysis, 555 and 542, Figures 192 and 193. 




118 KEBULAR LIFE. 

4. JSfon-annulating Nehulm and Stratified Rings. — 
The progressive changes of nebulji? seem to be toward the 
stellar condition. Not improbably, many nebulae, espe- 
cially small ones, shrink into single stars, as Sir William 
Herschel supposed. Some of the planetary nebulae may 
possibly contract indefinitely without breaking into separate 
nebulous fragments. In either event, they appear to 
undergo a sort of annulation. 

It seems more probable, however, that most nebulas 
break up normally into a large number of partial masses. 
I have indicated a process of curdling as a possible step in 
the stellation of a non-rotating nebula. Each separate 
mass may be regarded as embracing in some instances, 
material for a sun and planetary system. This idea, how- 
ever, supposes that a rotation comes into existence in each 
mass. How this could be generated while the physical 
conditions are such as to favor the segregation of the 
masses, and thus prevent that precipitation of mass upon 
mass which is the most obvious cause of nebular rotations, 
I am not able to understand.* I must leave the discrete, 
non-rotating nebula, if such really exists, for the further 
developments of science. 

As to rotating nebula?, I have shown that they tend to 
annulation. A ring of nebulous matter, if little disturbed 
by external perturbations, may rotate indefinitely around 
its centre of gravity. The process of shrinkage in a 
persistent rotating ring of nebulous or pulverulent matter 
would, in some cases, result in a stratification, or sepa- 

* 1 former!}' regarded nebular collisions as many times the most probable 
cause of rotations ; but later reflection leads ma more and more to the conviction 
that simple mutual attractions upon amorphous forms suspended in space, are 
competent to generate universal rotations. It becomes more and more apparent 
that rotation is inevitable^ and that it must exist even in the planetary and curd- 
ling nebulae. The latter are resolvable nebulse which nevertheless give a spec- 
trum of bright lines, and hence, must consist of nebulous matter in a discrete 
condition. Such is the nebula or "cluster" in Hercules. Even the separate 
masses of a curdling nebula must sooner or later rotate. 



SPHERATTON^ OF RIKGS. 



119 



ration of the ring into two or many concentric rings 
(Figure 30). The stratified condition might also arise, as 
Kant first suggested, from the different velocities of the 
outer and inner portions of a broad ring progressively 
disengaged. It is also quite conceivable that every annu- 
lar mass, separated after 
a secular interval, should 
consist originally of dif- 
ferential annuli dropped 
off in small consecutive 
elements of time. These, 
if ever existing, which is 
not probable, must nat- 
urally experience a strong- 
tendency to coalescence in 
groups, at the same time 
that their different angu- 
lar velocities might resist 
the coalescence together 

of rings differing much in diameter. Be the cause of 
stratification what it may, it seems to be at least an oc- 
casional incident of nebular life. A persistent example is 
actually noted in the rings of Saturn. 




Fig 30.— Stratification of a Nebulous 

EiNG. 



§ 4. SPHERATION OF RINGS. 



1. Disruption of a Ming. — Sooner or later, external 
perturbations or actual collisions must generally result in 
the breaking up of a nebulous ring. In some instances 
perturbation would develop undulations which, continu- 
ally exaggerated, would finally produce rupture, or destroy 
the equal distribution of matter around the ring. An 
increase of mass on one side, however caused, would 
draw still other matter toward it. The ring on the oppo- 
site side would become slender (Figure 31), and would 



120 



KEBULAR LIFE. 




-Nebulous Eixg Uxdergoixg 

RUPTUKE. 



finally part. The annular 
mass would now rapidly 
gather itself into a sphe- 
roid (Figure 32), which 
would continue revolv- 
ing in a path determined 
by the position of the 
transformed ring. It 
seems possible that such 
process of aggregation 
might take place at two 
or more points in a ring, 
and this is the view which 
was entertained by La- 
place. In such case, there would result a corresponding 
number of spheroids; but these would sooner or later co- 
alesce in one. No two bodies 
could continue permanently 
to revolve in one orbit. 

C. S. Cornelius, in an essay 
of much originality, has ad- 
vanced the opinion that the 
separated ring would attract 
to itself some neighboring por- 
tions of the abandoned nebu- 
lous spheroid. These portions, 
he assumes, would join the 
ring- with a smaller rotational 
momentum, and the union of parts thus differing in energy 
of rotation would strain the ring to such an extent as to 
rupture its continuity. Each of the resulting partial sphe- 
roids would rotate in the original direction. But the larger 
of these would eventuallv unite all the others in itself.* 




Fig. 32.— Spheratiox of a Nebu- 
lous Ring. 



* Vereinigte nun der sich ablosende Ring diirch Anziehung die zunachst 
angrenzeuden Theile der Dunstkugel mit seiner Masse, so musste derselbc ver- 



SPHEEATION OF RINGS. 121 

The breaking up of a set of concentric rings would re- 
sult in a corresponding number of rotating bodies, which 
would be likely, in some cases, to remain isolated. 

By some such means repeated a number of times, the 
entire nebula would be reduced to an assemblage of par- 
tial nebulous masses, all revolving in orbits about the 
original centre of gravity.* 

2. Rotation of Resulting Mass. — It may be set down 
as a necessary result that the mass derived from a ring- 
would possess a rotary motion about some axis. By an 
infinity of chances to one, the resultant of all the external 
forces acting upon it would not pass through the centre of 
gravity. But the mode of connection between the derived 
spheroid and the parent mass would be the principal de- 
terminative circumstance. The lines of interaction be- 
tween the two would be located nearly in the plane of the 
equator of the original mass; and hence the probable 
rotation would be in that plane. We have then to con- 
sider whether the rotation would be direct — that is, in the 
same direction as that of the primitive nebula — or retro- 
grade. 

The ring before spheration possessed a certain amount 
of breadth. Laplace conceived that the external and in- 
ternal zones of the ring would rotate with the same angu- 
lar velocity, which would be the case with a solid ring; 
but the principle of equal areas requires the inner zones to 
rotate more rapidly than the outer. The determination of 
the relative velocities of the outer and inner zones is the 



moge der abweichendeu Rotationsgeschwindigkeit und Schwungkraft der ange- 
zogenen Theiln, so wie audi in Folge von Moleculaikriiften seinen Zusammen- 
hang verlieren iind in mehrere Stiicke zerfallen. * * * Das grosste Bnich- 
sliick des Rlnges niochte nun insgemein die kleineren Stiicke herbeiziehen und 
Bie mit seiner JIasse vereinigen. {Entstehung der Welt, p. 18. Leipzig, 1870). 

*Tlie stability of a ring, while possible, is something with a high order of 
chances against it. See Maxwell : On the Stability of the Motion of Saturn's 
rings, and B. Peirce, Gould's AstronomicalJournal, ii, IT, 18. 



122 XEBULAR LIFE. 

solution of the problem of the direction of the rotation of 
the derived spheroid. 

I have maintained, when speaking' of the periodicity of 
ring-formation, that friction, cohesion, and mutual attrac- 
tions of the parts of a separating ring must exist to such 
an extent as to render annulation periodic. If I am cor- 
rect in this opinion, it is manifest that friction, cohesion, 
and mutual attractions of the outer and inner zones of the 
ring would tend to equalize the angular velocities of the 
outer and inner portions. Let us assume, in the first place, 
that the equalization of external and internal motions 
becomes nearly complete. The remotest side of the derived 
spheroid would then accomplish a revolution about the 
parent mass in the same time as the nearer side. The 
nearer side would remain turned toward the parent mass 
during the entire revolution. This is equivalent to saying 
the derived mass would complete one rotation on its axis 
while performing one revolution in its orbit. The motion 
would be direct. The relations assumed are the condition 
of direct rotary motion. 

If we had no concomitant interference to consider, it 
is manifest that the direct rotation thus inaugurated would 
be accelerated by subsequent cooling and contraction, and 
the primitive synchronism of axial and orbital motions 
would immediateh' cease to exist. As the final amount of 
acceleration in a rotating spheroid contracting in conse- 
quence of loss of heat, depends on the amount of contrac- 
tion, and this depends on the amount of matter, it is 
obvious that the final velocity of rotation must be propor- 
tional to the mass. Large masses in advanced stages of 
their existence should have a more rapid rotation than 
small masses in corresponding stages. All masses must 
experience acceleration proportioned to the total amount 
of contraction undergone. 

The derived mass might be of such magnitude as to 



SPHERATION OF RINGS. 123 

retain its nebulous state long enough, and acquire rotary 
acceleration enough^ to enter, on its own part, upon a 
process of annulation. This system of disintegration, so 
far as concerns the forces which inaugurated it, must con- 
tinue until the augmentation of paracentric force can no 
more become sufficient to equalize the sum of the force of 
gravitation and the resistance of rigidity. The whole his- 
tory of acceleration and disintegration is independent of 
the direction of the motion. 

The subsequent evolutions thus enunciated would begin 
immediately on the spheration of a ring, if no external 
interference were experienced. To this point I shall here- 
after return. 

Let us next consider what would happen if the relative 
velocities of the outer and inner zones of the nebulous 
ring should be determined in full accordance with the 
principle of equal areas. In this case, the velocity of the 
inner zone would as many times exceed that of the outer, 
as the square of its distance from the centre of motion is 
less than the square of the distance of the outer zone from 
the centre of motion. So far as this circumstance is con- 
cerned, the nearer side of the derived spheroid would tend 
to perform its circuit about the primitive centre in less 
time than the remoter side. But, as we assume all parts 
to be held together, the result would be a retrograde rota- 
tion of the derived spheroid. The subsequent cooling, 
contraction and acceleration would proceed exactly as in 
the case of direct motion. 

Now, reflection upon this subject has led me to the 
conviction that the physical relations accompanying the 
spheration of a ring are not such as to determine uniformly 
either direct or retrograde motion. Under certain circum- 
stances the motion would be direct; under other circum- 
stances, it would be retrograde. It seems probable the 
coasistency of a nebulous mass and its rate of condensa- 



124 KEBULAR LIFE. 

tion internally would be such g-enerally, that the actual 
relation of velocities of the outer and inner zones would 
be somewhere between uniformity and that determined by 
the principle of equal areas. 

Since we may fairly assume the influence of friction, 
cohesion and mutual gravitation of parts to have some 
real existence in a nebulous ring, there must be consti- 
tuted, so far, a tendency to equal angular velocities in the 
inner and outer zones, and a corresponding predisposition 
to direct motion. So far as the law of equal areas is con- 
cerned, there must exist a predisposition to retrograde 
motion. These two predispositions must always exist, 
and they must always contend against each other. The 
preponderance of the one will give direct motion; the 
preponderance of the other will give retrograde motion. 

But we understand the principle of equal areas is an 
absolute physical law whose action, disregarding mass 
(since in this question we may deal always with equal 
masses), is always with efficiency inversely proportional to 
the square of the radius vector. The measure of this 
efficiency is the difference of the squares of the radii 
vectores of the outer and inner zones of the ring. Against 
this contends a set of influences which vary with circum- 
stances. Friction will vary with the pressure upon the 
contiguous parts, and this will vary with the mass in a 
section of the ring. Cohesion will vary with tlie kind and 
state of the matter. The mutual attraction of parts will 
vary with the mass in the section and the distances of the 
centres of the partial masses. 

Under what circumstances will these variable influences 
attain a maximum? In other words, when will direct 
motion be most likely to ensue? Manifestly, when the 
nebulous matter is most condensed, and most acted upon 
by the attraction of the parent mass. That is, when the 



SPHERATIOX OF RINGS. 125 

progress of anuulation has reached somewhat toward the 
central portion of the nebula. When will the opposing 
principle of equal areas possess least efficiency? Mani- 
festly, when the rings are narrowest. That is, when the 
density of the nebula reduces the period during which a 
forming ring may continue to receive accessions. In other 
words, in the later stages of annulation. It is, therefore, 
in the later stages of annulating life that the predisposi- 
tion to direct motion is greatest, and the predisposition to 
retrograde motion is least. It is perfectly rational to sup- 
pose, finally, that the derived spheroids resulting from 
later evolutions should possess direct motion. 

These conditions are all reversed in the earlier stages 
of the annulating history of a nebula. In the peripheral 
portion of the nebula, diminished gravitation operates less 
efficiently in restraining the accession of matter to the 
forming ring, and thus allows the ring to attain greater 
breadth. In the primitive epoch also, the great tenuity of 
the matter implies diminished friction and cohesion, and 
correspondingly implies a more rapid contraction, and a 
greater prolongation of the period of ring-growth. It 
implies, in other words, a greater breadth of ring, and a 
greater efficiency of the principle of equal areas; and a 
correspondingly stronger predisposition toward retrograde 
motion. It is perfectly rational to suppose, finally, that 
the derived spheroids resulting from earlier evolutions 
should possess retrograde motion. 

This conception of physical relations renders it proba- 
ble that the same nebula would evolve earlier secondaries 
inheriting retrograde axial motions, and later secondaries 
inheriting direct axial motions. This state of things 
partially exists in our solar system. But the considerable 
deviation of the equators of the Neptunian and Uranian 
systems from coincidence with the plane of the sun's equa- 



126 XEBULAR LIFE. 

tor should cause hesitation in accepting the foregoing 
views as a full explanation of their anomalous motions.* 

*The rea!>oniDg here employed may be made a little more tangible by the 
use of algebraic notation. 

Let R' — radius of inner stratum of ring. 
R'''= radius of outer stratum of ring. 
V' = linear velocitj' of inner stratum of ring. 
v"= linear velocity of outer stratum of ring. 
Then, supposing the angular velocities of the two strata equal, we have 

V: V":: W : W \ .-. V'= V"%,. 

This is the condition of direct motion. 

But supposing the outer and inner strata to have velocities according to the 
law of equal areas, we have 

R"^ 

V : V" :: R"^ : R'2 ; .-. v'^V" ^ . 

This is the condition of retrograde motion. 

R' R"- 

When the value of v' is at a certain point between v" .^— and v" .f^r-^;, there 

ri" R' - 

will be no rotation. Let x represent the excess of that value over v" ^^, and 

R"2 

y, the excess of v" .^^ over the same value. Then 
„R' , „R"2 

This is the condition of no rotation. 
But any change in values which will make 
„ R' , . „ R"2 

will result in di?'ect motion. This inequation will arise 

(a) When R' increases or R" diminishes — that is, when the breadth of the 
ring diniinishes. 

(b) When R' and R" diminish equally in arithmetical ratio — that is, when 
they pertain to a smaller ring having the same breadth and rotary velocitj-. 

(c) When v" diminishes, the other quantities remaining constant, or R' and 
R" also diminishing in equal arithmetical ratio— a condition in the later aiauila- 
tion of a mass having great central condensation. 

Also, any change in values which will make 
„R' . „R"2 

will result in retrograde motion. This inequation will arise 

(a) When R' diminishes or R'' increases— that is, token the breadth of the 
ring increases. 

(b) When R' and R" increase equally in arithmetical ratio— that is, when 
they pertain to a larger ring having the same breadth and rotary velocity. 

(c) When v" increases, the other quantities remaining constant, or R' and 
R" also increasing in equal arithmetical ratio— a condition in the earlier annula- 
tions of a mass having great central condensation. 

From all which it appears that while direct motions must probably prevail 



SPHERATION OF RINGS. 127 

It ought to be remarked also, that the probability of 
retrograde motions in the earlier history of annulation 
would increase with the volume of the nebula. Because, 
in a larger nebula, the difference between peripheral and 
central condensation is greater, and here would exist a 
greater difference in the influences of friction and cohesion 
in the earlier and later processes of annulation. We 
should infer, therefore, that in a relatively small nebula 
all the rotations would be direct. This inference is exem- 
plified in the Saturnian and Jovian systems of satellites; 
and probably also in the Uranian and Neptunian, where 
direct motion would be motion in the direction of the 
rotation of the primaries. 

Some investigators of this subject have assumed the 
position that the primitive rotation of the derived mass 
must in all cases be retrograde.* They ignore, however, 
the influence of friction and cohesion. Others have at- 
tempted to show that retrograde motions either must or 
might arise in the earlier annulation-history, while direct 
motion would ensue in the later history.f The conclusion 
is the same which I have reached by a method which seems 
more intelligible and convincing. Professor Hinrichs 
shows that the rotary motion will be direct, zero or retro- 
grade, according as the primitive density of the nebula in 
the part where the orbit becomes located, was greater, 
equal to or less than a certain quantity depending on the 
position of the orbit in the ring, and on the law of varia- 
tion of the density. If the variation in density were zero, 

in the regions nearer the centre, retrograde motions may arise in the regions 
remoter from the centre. 

It may be added that the actual occurrence of direct motions in our system 
is evidence that the inner and outer strata of tlie corresponding rings did not 
possess velocities adjusted fully to the law of equal areas. 

* D. Kirkwood, Amer. Jour. Sci., II, xxxviii, 2^; D. Trowbridge, Afner. Jour. 
Set., II, xxxix, 25-6. 

t G. Ilinrichs, Amer. Jour. Sci., II, xxxvii, 51 ; M. Faye, Comptes Rendus^ xc, 
640. 



128 Js^EBULAR LIFE. 

all the derived spheroids would have direct motion. But if 
the density diminished from the centre, however slowly, 
then the earlier formed secondaries would have retrograde 
motion, and the later direct motion. The conclusion is 
based solely on relations of density, interannular spaces, 
and position of resulting orbit in the ring. 

Mr. Faye, adopting an analytical expression"^ for the 
law of increase of density toward the centre, determines 
that the linear velocities of the internal parts will go on 
increasing in diminishing ratio from the circumference to 
a certain distance from the centre, when the linear rotary 
velocities will begin to decrease. Thus he concludes that 
the annulating-life of a nebula would be divided into two 
periods, during the first of which the rotary motions of 
the derived masses would be retrograde, while during the 
other they would be direct. But it does not appear evi- 
dent that the superior linear velocity of the remoter parts 
would suffice as a sole cause for effectuating retrograde 
motions. Such'motion must result from a certain ratio of 
outer and inner velocities, and this depends, as I have 
shown, on the breadth of the ring and the influence of 
friction and cohesion. M. Faye takes no account of the 
influence of friction and cohesion, while, so far as I under- 
stand the subject, the possibility of direct motion at any 
stage depends on the preponderating influence of friction 
and cohesion. 

It is not necessary to assume that axial rotation would 
be impressed only by the forces already mentioned. If 
two or more spheroidal masses should result from the 
rupture of a nebulous ring, and should afterward coalesce, 
their impact must generate a rotation, as heretofore ex- 
plained. But such rotation would as probably be in one 



'('-M"jf) 



*Dll— ^y T7~r "li^rc D is the central density of the nebula, R the ra- 
dius of its equator, r the distance from any point to the center, n an arbitrary 
positive number, and /3 a very small fraction. 



SPHERATION OF lilKGS. 129 

direction as another, except so far as the synchronous 
rotation, always necessarily existing in the primitive stage, 
should predispose to a rotation in the established direc- 
tion.* In spite of this there ought to be some cases in 
which the motion would be retrograde, or the axis of 
rotation far from perpendicular to the plane of the orbit. 
In addition to this, it remains to be said that every exter- 
nal attraction experienced by the forming spheroid, until 
its form should have attained mathematical symmetry, 
would tend to inaugurate rotation, or change any existing 
rotation, under any of the conditions pointed out in dis- 
cussing the origin of nebular rotation in general. 

3. The Influence of Cosmic Tides upon the Rotation of 
the Derived &pheroid.\ — We come now to consider the 
interferences before alluded to. Supposing the derived 
spheroid to be affected by a motion of rotation, the ac- 
celeration of its rotation would not immediately proceed 
step by step with the progress of cooling and contraction. 
Such acceleration would be opposed by the prolate de- 
formation which would arise through the differential mo- 
menta of its own parts, and the differential attractions of 
the central residual mass exerted on a mass of such 
mobility of parts as the incandescent vapor which we are 
considering. By hypothesis, the centre of gravity of this 
new sphere is at such distance from the parent mass as to 
be poised between centripetal and centrifugal tendencies. 
The remoter point a. Fig. 33, must therefore experience 
an excess of centrifugal tendency in consequence of its 
greater velocity, and would only be retained by the attrac- 
tion of the derived mass. It would indeed tend to retire 
from c until the centrifugal force due to rotation about o 

* In this connection the various inclinations of the planetary axes in the 
solar system are somewhat suggestive. The inclination of Venus amounts to 
50°, while that of Uranus and Neptune is generally considered to be over 90". 

t The influence of tides in cosmical history will be more fully considered 
hereafter in connection with planetary vicissitudes. 
9 



130 



KEBULAR LIFE. 




Fig. 33.— Prolateness and Rotation 
OF THE Derived Spheriod. 



should be balanced by 
the central attraction 
directed toward c. On 
the contrary, the parts 
at h, having now the 
same angular velocity 
as the other parts, but 
a slower actual veloci- 
ty, the centripetal ten- 
dency w^ould be in 
excess, and they would 
extend toward o, until 
this excess should be 
counterbalanced by 
gravitation toward c* 
Concurrent with these actions w^ould be the difference of 
attractions exerted by the parent mass upon a and 5, 
raising veritable tides in those opposite regions. Thus, a 
prolate spheroid would come into existence, whose stabil- 
ity would persist for a certain period. But the contrac- 
tion of the mass and the increasing effort to accelerate 
the gyration might ultimately destroy the synchronism 
between axial and orbital motions. 

There is this further to be said of a prolate aeriform 
mass situated as described, and constrained toward accel- 
erated rotation. It must not be viewed as a rigid body. 
All its parts possess excessive mobility. The superficial 
particles at a, under an impulse to accelerated motion, 
would floio^ on the assumption of an effort toward direct 
motion, in the direction of the arrow, toward J, if the 
general mass were restrained from a consentaneous move- 
ment. Parts at h would experience a similar tendency 

* While this reasoning discloses a true cause of prolateness or tidal eleva- 
tion, it is not conceived to be the most efficient cause of tides, especially upon 
the larger of two spheroids tidally connected together and differing greatly in 
mass. 



SPHERATION OF RINGS. 131 

to flow in the same direction. Thus superficial currents 
would be established; and these would deepen and involve 
more and more of the whole mass. In proportion as the 
flow of these currents should be established and deepened, 
the attainment of accelerated rotation of the general 
mass would be accomplished; and ultimately the whole 
mass would possess a rotation more rapid than the orbital 
rotation. Thus, perhaps, might an axial rotation be ac- 
quired nearly corresponding with the acceleration due to 
the contraction of the mass after the earliest epoch of 
spheration. But the prolateness would never disappear, 
and would only diminish in proportion as the molecular 
mobility should diminish by condensation, by cooling or 
some other cause. Different sides of the derived spheroid 
would consequently be raised successively into a tidal pro- 
tuberance. The consequence of this would be a perpetual 
relative displacement of the different parts in respect to 
each other,* which might be compared with the effect of 
rolling an india rubber ball between the hand and a surface 
on which the ball is pressed. 

The prolate condition of the new spheroid may be con- 
templated without regard to the relative motions of its 
constituent parts. It hangs balanced by a support fixed 
at the centre of the forces acting upon it. It is manifest, 
therefore, that any new force applied to it, having a com- 
ponent making an oblique angle with c O (Figure 33), 
must, unless such component pass through the centre of 
inertia, disturb the equilibrium of the position of the body. 
In other words, the prolate axis, a h, would be inclined so 
as to make an angle with c O. The actual direction of 
the motion would be a resultant of this perturbative 
action and the existing strain toward accelerated rotation. 
It is supposable that this strain might be so nearly equal 

* I shall employ this principle iu explainiug the origin and phenomena of 
vulcanicity in the earth. 



132 l^EBULAK LIFE. 

to the synchronous tendency that the power overcoming 
this tendency would only need to be comparatively slight, 
and that, consequently, the actual movement of the mass 
would be about an axis very nearly normal to the plane of 
its orbit, and, on the assumption made, in the direction of 
the orbital motion. I see no ground for assuming that 
such a relation of perturbative and synchronizing forces is 
unlikely to arise in a nebulous spheroid resulting from the 
spheration of a nebulous ring. 

Should the disturbing action be temporary, the body 
would swing back to the position determined by the origi- 
nal forces; or rather, it would swing past that position 
and begin an oscillatory movement which would be per- 
petuated until interfered with by some other external dis- 
turbance. It is manifest that this oscillation of the line 
ah might be in any plane. If not exactly in the plane of 
the orbit, or in a plane at right angles with this, the 
motion might be resolved into two components, one lying 
in each of these planes. Thus would arise movements 
analogous to those known in astronomy as nutations and 
librations. It must not be supposed, however, that the 
longer axis of the figure would receive the whole of this 
motion, since attraction toward O, together with inter- 
molecular freedom of motion, would cause this axis to lag 
behind during every oscillation of the former axis away 
from the line c O. In other words, just so far as intermo- 
bility of parts exists, the prolate axis would be maintained 
in the direction cO; and it would be swung out of this 
direction only in proportion as the mass might have pro- 
gressed toward a state of rigidity. 

According to the conception here set forth respecting 
the formation of a prolate spheroid, the synchronism of 
orbital and axial movements might be destroyed only after 
cooling and contraction should have developed sufficient 
tendency to accelerated motion to overcome, in conjunc- 



SPHERATION" OF RIKGS. 133 

tion witli any perturbative action, the actions holding the 
line a h in its position. If, while this acceleration is be- 
coming developed, the mass should attain approximate 
rigidity, the superficial currents before mentioned would 
be arrested, and would cease to contribute their agency 
toward an increased rotation of the general mass; but, 
on the contrary, the crushing process of maintaining pro- 
lateness would be greatly opposed, and the prolateness 
would be correspondingly diminished, together with its 
resistance to heterochronous rotation. 

The conservation of synchronous motions would be 
promoted by an action not yet mentioned. Conceiving 
each tidal protuberance to be represented by a point at 
the apex, it appears that the one on the nearer side by 
being brought under an increased centripetal force will 
suffer a tendency to accelerated motion in its orbit. The 
effect of this would be to set up a retrograde rotary motion 
in the derived spheroid. On the contrary, the point at 
the apex of the anti-tide, by being brought under a dimin- 
ished centripetal force, will suffer a tendency to retarded 
motion in its orbit. The effect of this will also be to set 
u]) a retrograde rotary motion in the derived spheroid. 
This factor unites wnth intermolecular friction, cohesion 
and inertia in delaying the establishment of heterochron- 
ous motions. 

A rigid body, or any solid body approximately rigid 
and incompressible, possessing such prolateness as to 
result in synchronism of axial and orbital motions, could 
never have this synchronism destroyed except by a disturb- 
ance exerted from without. This, therefore, is a relation 
of orbital and axial motions which ought to result some- 
times in the progress of the history whose earlier chapters 
we are endeavoring to trace. It would be more likely to 
result in proportion as the process of refrigeration should 



134 N"EBULAR LIFE. 

be relatively more rapid. This would take place in nebu- 
lous masses relatively smaller. 

4. Ultimate Synchronism of Axial and Orbital 3fo- 
tions. — It should be mentioned in this connection, that 
synchronous movements having been once overcome, in 
the early stage, there would be felt a tendency to their 
reproduction, under certain conditions, during a later stage 
of development. While the nebulous condition exists, 
contraction would be rapid and great in amount. The 
resistance offered by prolateness to the destruction of syn- 
chronism, would perhaps, therefore, in all cases, be com- 
pletely overcome, and a rapid rotary motion would be a 
nearly uniform incident in the history of cooling. But, 
as the tidal protuberance, even if solidification should 
ensue, can never cease to exist, its influence in opposing 
rapid rotation will never be removed. When, therefore, 
the rate of contraction and consequent tendency to accel- 
erated rotation has been much reduced by an advanced 
stage of cooling, or by incrustation or solidification, the 
resistance of the tidal prolateness, which does not diminish 
accordingly, must again tend to equilibrate and neutralize 
the rotating tendency. This effect, upon a globe perfectly 
solidified, would probably reach a maximum in those cases 
where fluids like oceans should rest in basins with solid 
barriers against which the fluid tide could act. Thus the 
condition of synchronous axial and orbital revolutions is 
also an incident in the advanced stages of the cooling- 
history. 

5. Summary. — We have thus been occupied with 
the difficult question of the direction and velocity of the 
rotation which would arise in a spheroid resulting from 
the spheration of a nebulous ring detached from a central 
rotating mass. The conclusions reached may be sum- 
marized as follows : 

(1.) Rotation would arise with the process of sphera- 



SPHERATION" OF RINGS. 135 

tion, and its axis would most probably be at right angles 
with the plane of the nebular equator. 

(2.) The direction of the rotation would be determined 
by the relation of the velocities of the outer and inner 
zones of the ring. 

(3.) If all parts of the ring rotated with nearly the 
same angular velocity, the resulting rotation in the 
spheroid would be direct. 

(4.) If the inner zone rotated with increased velocity, in 
accordance with the law of equal areas, the rotation would 
be retrograde. 

(5.) Friction and cohesion and mutual attraction of parts 
would have a tendency to equalize angular velocities, and 
thus to create a strain toward direct motion. 

(6.) If this strain were unequal to the tendency toward 
motion under the law of equal areas, the rotation would 
be retrograde; if it equalled that tendency there would 
be no rotation; if it exceeded it, the rotation would be 
direct. 

(7.) The strain toward direct motion would be least 
when the nebulous matter is tenuous, for then friction and 
cohesion would be least, and the influence of gravitation 
would be least felt. The strain toward retrograde motion 
would be greatest when the ring is widest, for then the 
acceleration of the inner zone is greatest. The conditions 
of least strain toward direct motion and greatest toward 
retrograde motion would concur in the earlier annulating 
stage of the nebula. 

(8.) The strain toward direct motion would be greatest 
when the nebulous matter is most dense, for then friction 
and cohesion would be greatest, and the influence of 
gravitation would be most felt. The strain toward retro- 
grade motion would be least when the ring is narrowest, 
for then the acceleration of the inner zone would be least. 
The conditions of greatest strain toward direct motion 



136 KEBULAR LIFE. 

and least toward retrograde motion concur in the later 
annulating stage of the nebula. 

(9.) The rotation, if direct, would at first probably be 
synchronous with the orbital revolution, and the derived 
spheroid would be prolate. This prolateness would tend 
to persist, (a) In consequence of the imperfect intermo- 
bility of parts in the spheroid, (b) In consequence of an 
adjustment of parts having different densities, so that the 
most and least dense would be ranged about the poles of 
the prolate axis. 

(10.) The progressive contraction of the derived spheroid 
would result in a perpetual tendency to rotate more 
rapidly; and this tendency might overcome the tendency 
to synchronous movements. This would be the more 
likely as the latter tendency would diminish with the 
increase of the square of the interval between the centres 
of gravity of the derived and original masses. 

Memorandimi. — This interval would increase, [ci) By 
the progressive shrinkage of the central mass. {IS) As a 
consequence of the diminished centripetal force, (c) As 
the result of any eccentric motion which may, in some 
cases, have been imparted to the derived mass at the epoch 
of its separation from the primitive mass. 

(11.) In a derived spheroid possessing great, but un- 
equal, intermolecular mobility, the establishment of super- 
ficial currents, gradually deepening and involving the whole 
mass, would tend to destroy primitive synchronous move- 
ments. 

Memorandum. — The prolateness of the derived mass 
would, however, be maintained, and would diminish only 
in proportion as its rigidity should increase. 

(12.) Perturbative action having a component making 
an oblique angle with the prolate axis might overcome any 
preponderating tendency to synchronous motions. 

(13.) In a rigid prolate body synchronously rotating, 



SPHERATION OF RINGS. 137 

only external perturbative action couid ever destroy the 
synchronism. 

(14.) Rotation would also be caused by the inevitable 
ultimate coalescence of the two or more masses into which 
it is supposable that an unstratified nebulous ring might, 
in some instances, be separated. The discordant positions 
of the rotational axes resulting from this cause are, how- 
ever, not distinctly apparent among the phenomena of the 
solar system. 

(15.) Synchronous motions would result again, in the 
ulterior history of the derived spheroid, through the con- 
tinued action of tidal friction. This result, though favored 
by the existence of fluids on the surface, would not be 
permissively conditioned upon it, since all tidal motions in 
a spheroid whose constituent parts are not perfectly free to 
move, are, by so much, constrained in the direction opposed 
to those motions, the tidal effects are delayed and the tidal 
action becomes thus a constant effort to rotate the spheroid 
in the direction of the tidal progress, that is, in a direc- 
tion contrary to the normal rotation of the spheroid.* 

6. Arrangement of Heavier Matters on the Derived 
Spheroid. — In all stages of the derived spheroid there 
would be a tendency of the heavier parts to accumulate 
on the side nearest the central attractive body. There 
maybe a condition of matter in which diversified densities 
have not been attained. There is also, probably, a stage 
of nebulous history in which the intermobility of parts 
prevents adjustment of portions in accordance with densi- 
ties. But assuredly, a time sooner or later arrives when 
diversity of densities not only exists, but the conditions are 
such that the positions of the parts must be determined 
by their relative densities. While synchronistic motions 
exist, there will be two forces acting toward the determi- 

* The subject of tidal action will be resumed and studied in greater detail in 
connection wiih planetary evolution. 



138 KEBULAR LIFE. 

nation of those relative positions. One is the central 
attraction toward the centre of orbital motion; the other 
is the centrifugal tendency resulting from the orbital mo- 
tion. The nearest parts experience most of the centripe- 
tal tendency, and the remotest parts, most of the centrifu- 
gal tendency. The centripetal force tends to bring the 
denser parts to the nearer side, and the centrifugal force 
tends to transfer them to the remoter side. Unless the 
excess of the centripetal force on the nearer side exactly 
equals the excess of the centrifugal force on the remoter 
side, the heavier parts must tend toward one extremity of 
the prolate axis. Whichever be the side toward which they 
settle, the resulting distribution of the matter must consti- 
tute a resistance to the disturbance of synchronistic motions. 

The factors entering into a determination of the ques- 
tion to which side the heavier parts w^ould tend are, the 
mass of the central body, the distance between its centre 
of gravity and that of the derived spheroid, the length of 
the prolate axis of the derived spheroid and the velocity of 
motion in its orbit. 

In any particular case, where the mass of the central 
body and the length of the prolate axis remain constant, 
the relation of the differential centripetal and centrifugal 
forces to each other will vary, on condition of uniform 
angular velocity of rotation, with the distance between 
the centres of gravity of the two bodies. But the differ- 
ential centrifugal tendency, on the conditions assumed, 
remains constant.* On the contrary, since the centripetal 

* The centrif ngal tendencies at the nearer and remoter poles of the prolate 
axis being represented by F' and F'\ and the distances of these poles by d' and 
d'\ we have for the angular velocity 0, by the principles of mechanics, F"—F' 
= d"6'^~d'6-^ Now suppose the spheroid to be placed at a different distance 
from the central bod3% so that d'= d' ± n and d"—d" ± n. Letting/' and/" rep- 
resent the centrifugal tendencies at the poles of the prolate axis, in the new 
position, we have, for the same angular velocity as before,/"— /'= (cfi n)02_ 
(d' ± n) 6"^- d"e'i - d'0'^= F"- F-*. Hence the differential centrifugal tendency 
remains constant. 



SPHERATIO^r OF RINGS. 139 

force varies inversely as the square of the distance, the 
differential centripetal tendency increases with the distance 
between the two bodies. Hence if, at any distance, the 
differential centripetal and centrifugal tendencies are 
equal, at a less distance the centrifugal would preponder- 
ate, and at a greater, the centripetal would preponderate. 
Where the orbital motion at different distances is in con- 
formity with Kepler's third law, the angular velocity, and 
hence the differential centrifugal tendency would be in- 
creased with shortening of the distance; and accordingly, 
the differential centripetal and centrifugal tendencies 
would not diverge as rapidly (with a given rate of change 
in distance), as when, according to our first supposition, 
the angular velocity remains constant.* 

7. Orders of NehuliB. — Let us remember that our 
speculations thus far concern nebulae; and that the segre- 
gation of parts results in a system of nebulous masses, 
each of which in turn may be destined to repeat the evo- 
lutions of the parent nebula. Consider then, one of these 

* The equation of diflEerential centripetal and centrifugal tendencies presents 
the following relation among the values involved: 

Let g — gravity at the central body's surface, assumed to be a sphere without 
rotary motion. 
d' and d"= distances from centre of gravity of the central body to the 

nearest and remotest poles of the prolate axis. 
V' and V"— the linear orbital velocites respectively of these two poles. 
R = radius of central sphere. 
Then the condition of equal differential centripetal and centrifugal tendencies 
gives 

V'"^ _1T^_ RJ _ J?2 

d" ~ d' "Va V'2' 
But since v"^- — jj^, we have 

rf'-irf" d' •' \d''' rf"2/ 
Whence t- '= ^ [ g{cl"-\- d>) ]*• 

Also, since the angular velocity ^= j,, 



^= A; [9(d- + d^)]*, 



140 NEBULAR LIFE. 

partial nebulae. Though presenting but a small disc, at 
the enormous distance from which we gaze upon it, we 
must suppose its diameter greater than that of our solar 
system. It is still in large part an incandescent vapor. 
There was a time when the matter of our solar system 
was one of these partial nebulae, or perhaps an original 
growth which had never attained larger dimensions, or 
perhaps again, one of the segregated masses of a non- 
rotating nebula. Many of the stars in our firmament 
represent other nebulas of the same order, out of which 
have emerged the stars and the planetary systems which 
probably circle around them. It was the speculation of 
Kant, and the original conception of Sir William Herschcl 
(though he did not so distinctly enunciate the agency of 
rotation) that at periods incalculably remote, an enormous 
system of partial nebulae had issued from that grand uni- 
versal nebula which contained all the matter of our firma- 
ment of stars and planets. This firmament, as they 
thought, was possibly once a nebula, like those other thou- 
sands of nebuL^ which we believe to have advanced varying 
distances on the way to completed stellation. Kant con- 
ceived that it performed then a stupendous gyration about 
an axis. Even now, that gyration should be continued. 
The idea is not entirely fanciful; for astronomers have 
shown that all the stars, as a rule, are actually in motion; 
and Maedler believes that he has rendered it probable that 
our sun has Alcyone in the Pleiades for the centre of its 
orbit, and consumes 180 millions of years in completing a 
single revolution. If a nebula requires 180 millions of 
years for a single rotation, what change of position could 
we expect to detect in the brief interval since the con- 
struction of Sir William Herschel's great telescope? 

It must be soberly said, however, that there is com- 
paratively little ground for the opinion that our entire 
firmament is now in a state of gyration about a common 



SPHERATION OF RINGS. 141 

centre. In such case there would be more consentaneous- 
ness in the movements which have been actually traced 
among the fixed stars. There is no conceivable system of 
relative positions and velocities about a common centre 
which would develop the seemingly sporadic movements 
which we witness. Undoubtedly every star is in motion; 
and undoubtedly every star's motion is in obedience to the 
laws of central forces. Undoubtedly the sun and solar 
system are moving majestically across the spaces which 
separate star from star. It is shown also that many coup- 
lets and larger groups of stars are physically connected; 
and that most of the stars in certain regions of the heav- 
ens possess a common motion; but we have not, as yet, 
good inductive ground for affirming a common rotary 
motion of our firmament, or its derivation, by the annula- 
tion process, from a general firmamental nebula. There 
is more ground for the belief that each star is the residual 
centre of a distinct nebular mass, by whatever process iso- 
lated. We may therefore reasonably proceed to contem- 
plate the evolution of a solar nebula, regardless of the 
nature of its origin or previous transformations. This 
brings us to the question of the primitive history of a 
solar system. 

But we pause here in the midst of our speculations. 
The very firmament is careering in infinite space, while we 
ponder on its constitution and history or turn to our ma- 
terial occupations. Our comfortable homes, while we dine 
or sleep, are rolled through space at the rate of seven hun- 
dred miles an hour by the diurnal rotation of the earth. 
During the same time they are transported sixty-eight 
thousand miles by the movement of the earth in its orbit. 
Then the sun, with his entire family of planets, is sweep- 
ing through immensity, toward the constellation Hercules, 
with a velocity which, if equal to that of Arcturus, is two 
hundred thousand miles an hour. And lastly, there must 



142 NEBULAR LIFE. 

be some common motion of translation of the whole inex- 
tricable maze of moving stars, and with a velocity to which 
fancy may assign what rate it pleases without restraint 
from science. This mighty waltz of cosmic dancers is joined 
by the gauzy nebulae, animated also, like our firmament, 
by their own internal motions. In the midst of this uni- 
verse of seething movements is our appointed home. The 
mind uplifted in the effort to contemplate them and grasp 
their method, grows giddy and impotent. How sublime 
these activities ! To what a numerous and lofty compan- 
ionship does our little planet belong ! Hard it seems to 
be imprisoned here while the realm of the universe tempts 
us to its exploration. How can a human soul content 
itself to roll and whirl through space during its mortal 
days, and eat and sleep and trifle, like rats in a ship at sea, 
without wondering where we are and whither we are bound ? 



PART 11. 
PLANETOLOGY, 



CHAPTER I. 
ORIGIN OF THE SOLAR SYSTEM. 

Theoriarum vires, arcta et quasi se mntuo sustinente partium adaptatione, 
qua, quasi in orbcm coha^rent, firmantur.*— Bacon. 

Erst, space was nebulous. 
It whirled, and in the whirl, the nebulous milk 
Broke into rifts and curdled into orbs — 
Whirled and still curdled, till the azure rifts 
Severed and shored vast systems, all of orbs.— David Masson. 

I HAVE presented, in the preceding chapters, some of 
the evidences of the wide diffusion of world-stuff 
through space. We have no warrant whatever for affirm- 
ing its diffusion '' through infinite space"; nor can we 
rationally speak of any particular condition of this matter 
at any absolute "beginning." Nor can we affirm that it 
was distributed "uniformly"; nor that its tenuity was 
any number of thousand times "greater than that of 
hydrogen." It suffices to recognize the evidence that the 
cosmic matter which we now see a^oTeofated in worlds 
existing in various stages of development from a conceiv- 
able and rational starting point, was once widely diffused, 
and probably cold; and that by the mutual attractions of 
particles and masses, much of this matter became gathered 
into aggregations of vast magnitude. 

I have also attempted to show that the further opera- 
tion of gravity would tend perpetually to the further 
aggregation of these masses, and that their collisions 
would result in the development of intense heat. I have 

*The strength of theories is established by their compact and mutually 
sustaining coadaptation of parts, by which they cohere as in an arch. 
10 145 



146 ORIGIN- OF THE SOLAR SYSTEM. 

shown that rotary motion must have been also a result of 
such collisions; and must also have been generated by 
mutual attractions without the occurrence of collision. I 
have traced the further consequences of the rotation of a 
heated globe of nebulous matter, and have pointed out the 
necessity, in some cases, of a process of annulation, and 
the subsequent gathering of the rings into spheroidal 
masses rotating on their axes and revolving in orbits about 
the residual mass.* The process, as described, results in 
breaking up a great firmament al nebula into a large 
number of partial or solar nebulse; and it is one of these, 
or at least a nebula of this order of magnitude, which we 
are to follow further in the course of its evolution. 

It is not implied that all solar nebulae have been thus 
derived. It cannot be doubted that many nebulae are of 
magnitudes so small comparatively that they condense 
directly into suns and planets. They have never been of 
any higher order than solar nebulie. Whatever its ante- 
cedent history, it is the solar nebula to which attention 
is now directed. 

Being a nebulous mass essentially identical, except as 
to magnitude, with the firmamental nebula which we have 
been considering, it is evident that all its nebulous history 
must be essentially such as we have already traced. It 
only remains, therefore, to continue to follow the evolution 
in a case in which a nebulous a'lobe condenses directlv to 
the solar and planetary conditions. What needs to be 
said to make this part of the process plain to the reader 
can perhaps be best presented in the form of a citation of 
actual phenomena which find their best explanation in a 
nebular evolution; and then a discussion of the various 

* Should the reader feel interested in further views on the origin of clusters 
and nebulae, he may consult memoirs of Prof. Stephen Alexander in Gould's 
Astronomical Journal, vol. ii, 1852; as also those of Sir William Herschcl as 
cited in Part IV, ch. iii, § 2, of the present work, and the coincident views of 
Arago in Astronomie populaire. 



VERIFICATION OF THE NEBULAR THEORY. 147 

objections wnich have been urged against the theory by 
various classes of persons. 

§ 1. VERIFICATION OP THE NEBULAR THEORY FROM 

PACTS. 

1. Observed PhenoDiena of the Solar System lohich 
accord lolth the requirements of the Nebular Theory, 

A. DEMONSTRATIVE PHENOMENA. 

(See Works on Astronomy.) 

L The planets all move in their orbits in the same 
direction. 

2. The sun rotates on his axis in the same direction as 
the planets revolve in their orbits. 

3. All the planets, except Uranus and probably Nep- 
tune, rotate on their axes in the same direction. 

4. All the satellites revolve in their orbits in the same 
direction, except those of the planets Uranus and Nep- 
tune. 

5. The moon rotates on its axis in the same direction; 
and no satellite is known to rotate in the opposite direc- 
tion. 

6. The planes of all the planetary orbits are nearly 
coincident. 

7. The plane of Neptune's orbit is almost exactly coin- 
cident with the invariable plane of the solar system. (See 
§3,1.) 

8. The planes of all the planetary orbits in the course 
of their secular oscillations approach nearly to coincidence 
with the invariable plane; and the orbits of Venus, the 
Earth and Mars attain to complete coincidence. (See 
§3,1.) 

9. The planes of the secondary orbits are all nearly 
coincident with the planes of the equators of their pri- 
maries. 



148 ORIGIJ^ OF THE SOLAR SYSTEM. 

10. The plane of the sun's equator is nearly coincident 
with the invariable plane of the solar system. 

11. The sun is the centre of motion of all the planets. 

12. Every system of satellites has one primary for its 
centre of motion. 

13. The orbital paths of the planets and satellites vary 
but little from circles. 

14. The larger planets have the greater number of 
satellites because greater mass would prolong the period 
of mobility of parts, and thus the possibility of annula- 
tion. 

15. The angular and also the actual velocities of the 
planets and satellites in their orbits increase with the 
decrease of their mean distances from their centres of 
attraction. 

16. The Saturnian system still retains an example of 
the ring-condition. 

17. The Earth furnishes evidence of intense internal 
heat, and other evidences of a general temperature in 
ancient times, sufficiently high to fuse rocks at the sur- 
face. (See chap. Ill, § 1, 1.) 

18. The superposition of unaltered sedimentary rocks 
over metamorphic sedimentary rocks implies a process of 
cooling. (See works on Geology.) 

19. The animal and vegetable forms fossilized in the 
older rocks prove an ancient higher temperature for the 
terrestrial climates. (See Sketches of Creation and works 
on Geology.) 

20. The oblateness of the other planets implies a for- 
mer state of fluidity in them. 

21. The crater-like forms seen upon the surface of the 
moon indicate a former intensity of igneous action. 
(Chap. Ill, § 2, 3.) 

22. The absence of air and water from the moon indi- 
cates a state of complete refrigeration. (Chap. Ill, § 2, 5.) 



VERIFICATION^ OF THE KEBULAR THEORY. 149 

23. The cloud-enveioped condition of Jupiter, together 
with some indications of inherent luminosity, implies a 
temperature higher than that of the earth; and this may 
be supposed inherited from a past still more highly heated 
condition. A less advanced stage than that attained by 
the earth would be attributable to the vastly greater mass 
of matter in that planet, which would demand vastly more 
time to reach a cooled and habitable condition. (Chap. 
Ill, §5.) 

24. The substances which enter into the constitution 
of the sun are the same as those in the earth. (See Young 
on The Sun; Secchi : Le Soliel ; Schellen : Spectral 
Analysis, etc.) 

25. The composition of meteorites coming from the 
planetary spaces is terrestrial, and points to the general 
inference that all the bodies occupying the planetary spaces 
have the same composition as the earth and the sun. (See 
Meunier: Xe Ciel Geologique, and works on meteorites.) 

26. The planets and satellites all move about their cen- 
tral bodies with velocities so varying with the distance 
that the radius vector of each body describes equal areas 
in equal times. 

27. Our satellite always turns the same side toward the 
earth; and so far as we know, all the satellites of our sys- 
tem turn always the same side toward their primaries. 

28. The sun still exists in a nebulous condition so far 
as exposed to our inspection. 

. B. PHENOMENA PROBABLY CONFIRMATORY. 

29. The period of rotation of Saturn's rings is less than 
the axial rotation of the planet. 

30. The orbital velocities of the planets conform to the 
third law of Kepler instead of being in the ratio of the 
squares of the mean distances from the sun. (See § 2, 
Objection 4.) 



150 ORIGIN OF THE SOLAR SYSTEM. 

31. The ratio of the radii of gyration of the successive 
spheroids in the development of the Jovian system, to 
the actual mean distances of the Jovian satellites, is less 
than the corresponding ratios in the original planetary 
spheroids to the actual mean distances of the planets from 
the sun. 

32. The rate of axial rotation as we recede from the 
centre of motion of the system toward the periphery is 
increasingly more rapid (p. 165). The only exception is 
Jupiter, which rotates 36° an hour, while Saturn rotates 
only 34°. 5 an hour. (See Part I, ch. ii, § 4, 2.) 

II. Observed Phenomena not belonging to the Solar 
System \ohich accord icith the requirements of the Isfebidar 
Theory. (See Part I, ch. ii.) 

33. The nebula and other cosmic bodies exist in a 
nebulous state. 

34. The ring condition actually exists in certain 
nebulfe. 

35. Spiral and other nebulous forms indicate a state of 
rotation. 

We may cite in addition the brilliant experiment of 
Plateau.* 

All the foregoing phenomena observable within the solar 
system are, at least to the 28th, f so obviously conform- 
able to the requirements of the nebular theory that prob- 
ably no reasonable person will maintain that they present 
any difficulties. Now what must be said in view of such a 
catalogue of coincidences? They show at least, that all 
parts of our system must have had a common origin and a 

* J. Plateau : Memo'ire sur les phenoinenes que prisente une masse liquide libre 
et soustraite a I'action de la j)esant€)ti\ Nouveaux inemoires de rAcademie de 
Brnxelles, xvi. 1843, translation, Experimental and Theoretical Researches on the 
Figures of Equilibrium of a Liquid Mass Withdrawn- from the Action of 
Gravity, etc., Smithsonian Reports, 1863. 

t Prof. Stephen Alexander enumerates 62 "consistencies" or connrmations 
of the nebular theory (Smithsonian CoatribvUions xxi, Art. I, pp. 80-91). 



VERIFTCATION^ 01" THE KEBULAR THEORY. 151 

common history. If our earth has had a cosmic history, 
then that history involved all the other bodies of our system. 
Unless we choose to abandon all scientific method, and 
dogmatically assert that each world is the product of 
immediate creation, and deny that the plan which embraces 
their forms and movements shows any physical relation 
among them, we must seek for a theory of their past 
history v/hich will coincide in all these twenty-eight par- 
ticulars with the facts of observation. But a physical 
relation exists among all the parts of the solar system in 
human times; they are acting mutually upon each other; 
new positions and conditions are daily arising out of these 
mutual actions. We have seen a brief chapter of cosmical 
history enacted during the period of our observations; and 
the denial that this history stretches back into prehistoric 
and remoter times is a folly only equalled by that of a man 
who should stand on the banks of the Mississippi at New 
Orleans, and declare that the stream had no existence 
northward beyond the range of his vision. The parts of 
the solar system are physically connected in human times; 
and he who would deny that the history of such connection 
stretches into a remote past is incapable of reasoning on 
the subject. 

Now, if the real history whose outcome we look upon 
is a history of physical actions and reactions, what concep- 
tion can be formed of the particular nature of that history 
which will be more conformable to the leading facts of 
observation than the conception of an original nebula, 
rotating and cooling, and evolving progressively the inci- 
dents of such a process ? With so extended a catalogue 
of coincidences, a mere hypothesis ought to be regarded 
as a highly probable representation of the truth; unless 
some grand phenomenon remains to be accounted for, or 
some strictly crucial test dissipates the accumulated prob- 
ability in its favor. 



152 ORIGIJ^ OF THE SOLAR SYSTEM. 

I hear it said that these grandly outlined events are 
only a dream — a poetic creation, without the possibility 
of a demonstration. Well, if no more could be said, I 
am prepossessed by them, as the best and most plausible 
conjectures which could be made by the wisest of men. 
Until some objector can put forth a more probable concep- 
tion of that past history which has been so real, I deem it 
wise to pay respect to a conception which has been grow- 
ing in esteem for three quarters of a century. Let it be a 
mere hypothesis; it may be one ripened into an imperish- 
able doctrine. Gravitation was a mere hypothesis once — 
and once even an abandoned hypothesis. That the planets 
move in ellipses was Kepler's hypothesis; but now it is 
demonstrated. Is it said, the nebular hypothesis cannot 
be demonstrated? It is all but demonstrated to-day; and 
he who doubts is more credulous than he who believes. It 
is all but demonstrated by the three dozen coincidences 
which I have enumerated. And it is all but demonstrated 
by the rigorous processes of mathematics which so long 
since gave a rational basis to Kepler's laws. 

Yet, in the presence of so many coincidences and con- 
firmations; with the great weight of almost unanimous 
scientific opinion for an indorsement, we find such a judg- 
ment as the following on record in a work which is still 
recent: "We are obliged to conclude that the nebular 
theory lacks all the elements of credibility. It is at vari- 
ance with astronomical facts. It is destitute of philo- 
sophical consistency. It assumes everj'thing that ought 
to be demonstrated. It deals in glittering generalities 
where it ought to go into minute details. It ignores the 
mathematical relations of forces and effects. In fine, its 
data are intangible, incongruous and impertinent to its con- 
clusions. Never in the history of science was theory more 
pretentious. Never did theory less justify its preten- 



OBJECTIONS FROM PLANETARY MOTIONS. 153 

sions."* This language is emphatic and unreserved. 
Every word deserves to be italicised. This is the daring 
indictment drawn up against the good judgment of such 
astronomers and physicists as Laplace, Sir John Herschel, 
Helmholtz, Mayer, Tyndall, Sir W. Thomson, Clerk Max- 
well, Clifford, Croll, Huggins, Lockyer, Arago, Oersted, 
Becquerel, S. C. Walker, Benjamin Peirce, B. A. Gould, 
D. Kirkwood, J. C. Watson, G. Hinrichs, D. Trowbridge, 
S. Newcomb, C. E. Young, J. E. Hilgard, Joseph Leconte 
and a host of other names of similar authority in these 
and other departments of natural science. How superior 
must be the knowledge and the penetration of the indi- 
vidual who could brino; such an indictment against such 
an array of honored name's. And how clear and demon- 
strative the apprehension of the grounds of an indictment 
presented with such unruffled assurance of infallibility. 

§ 2. OBJECTIONS BASED ON RELATIONS OF PLANETARY 
MOTIONS. 

Let us now examine the phenomena which by one and 
another have been cited as incompatible with the nebular 
theory. 

1. Retrograde Motions.^ — The satellites of Uranus re- 
volve in a plane which makes an angle of 98^^ with the plane 
of the ecliptic. That is, the system is tilted up until it is 
8° beyond a right angle with the ecliptic, and the satellites 
thus have an apparent retrograde motion. Similarly, the 

* Rev. W. Slaughter : The Modern Genesis p. 290. We might offset this bold 
arraignment by the following passage from an authorit}^ of high and recognized 
standing as a logician: "'There is thus in Laplace's theory/' says John Stuart 
Mill, '■'■ nothing hypothedcal; it is an example of legitimate reasoning from a 
present effect to its past cause, according to the known laws of that cause ; it 
assumes nothing more than that objects which really exist, obey the laws which 
are known to be obeyed by all terrestrial objects resembling them " (System of 
Logic, Am. ed., p. 299.) 

tM. Faye, Comptes Hendus, xc, pp. 566-71, March, 1880; Rev. W. B. Slaugh- 
ter: The Modern Genesis, 103-109. 



154 ORIGIK OF THE SOLAR SYSTEM. 

plane of Neptune's satellite is tilted over 145°, so that it 
seems to have a retrograde motion in an orbit inclined 35° 
to the plane of the ecliptic. Now, nothing is more natu- 
ral than to suppose that a partial inversion of these sj-s- 
tems has taken place. These inclinations, in fact, are 
only extreme cases of the inclination which characterizes 
all the orbital and equatorial planes of our system. The 
satellites of Saturn have generally an inclination of 28°, 
and one of the Asteroids has an inclination of nearly 35°. 

(1.) It is entirely conceivable that both the Uranian 
and Neptunian systems should have suffered an overturn 
through the influence of some powerfully attracting body 
passing in the neighborhood. If this occurred before the 
planetary nebula had commenced annulation, then the 
motions of its later-formed satellites would conform to the 
plane of the planetary rotations. If it occurred after the 
satellites were formed, their orbits might depart very far 
from the equatorial plane of the planet. It is even con- 
ceivable, in this case, that the planet's rotary motion 
might be direct while the orbital motions of the satellites 
are retrograde. The influence of such disturbing body 
may also have been felt by the Saturnian system, which 
shows an extraordinary inclination, while the planets suc- 
cessively more remote have been successively more dis- 
turbed. 

The accompanying figure (Figure 33) will illustrate a 
possible method of the overturn of a system after the 
formation of the satellites. It represents a planet in its 
orbit, and surrounded by the orbit of one of its satellites. 
The latter orbit is originally coincident with the plane of 
the planetary orbit as shown in B Na A N. But suppose 
when the satellite is at A, an attractive influence to be 
felt from the direction C A; one component of this force 
would act in the direction A G, in the plane of the orbit, 
and would not alter the inclination of the orbit; but the 



OBJECTION'S FROM PLAKETARY MOTIONS. 155 

other would act at right angles with this, in the direction 
A F, and would tend to carry A toward F, but the attrac- 
tion of the planet would bring A toward the position A'. 
The satellite would pass on in its orbit, but upon its 
return to the vicinity of the position A, a further impulse 
would be felt. This would be repeated again and again, 




Fig, 34. Inversion of the Orbit of a Satellite. 

as long as the disturbing body should remain in the same 
general direction. It is true that the satellite would be 
attracted throughout its whole course, and at B the effect 
would be a partial restoration of the original position of 
the orbit; but the influence at B would be less than at A, 



156 ORIGIX OF THE SOLAR SYSTEM. 

because its distance from the disturbing body is greater; 
and hence the residual effect upon A would be due to the 
difference of the attractions in the two positions A and B. 

It is necessary 'to trace this effect somewhat farther. 
Had the satellite no inertia, the disturbing influence would 
turn its orbit only so far as to bring the plane into coinci- 
dence with the direction of the influence C A' B'. But 
the momentum acquired will carry the satellite beyond 
that point. If the influence still persists, the orbit will 
return and will thereafter oscillate slightly on both sides 
of the plane of coincidence. But if the influence dis- 
appears, or if an influence from another direction D A' 
arises, the motion of the orbit may continue until its angle 
with the plane of the planetary orbit exceeds a right angle 
by any amount. 

Now, suppose, before the satellite's orbit has been 
changed in position, an observer on the earth looking 
from the direction E, sees the satellite at B, moving in the 
direction of the arrow; call this direct motion. But sup- 
pose that afterward, when the orbit has been tilted so that 
the satellite on its passage through the point A" nearest 
the earth shall again be seen from the direction E, it is 
evident that its apparent motion (in the direction from the 
node N to the position A") will be the reverse of its 
former motion. This would be retrograde. But the 
satellite has continued to revolve in the same orbit and in 
the same direction, that is from the corresponding posi- 
tions B, B' and B" toward the node N, and from N toward 
A, A' and A", which represent the same point in different 
positions of the orbit 

One thing more; the action of the disturbing force is 
not likely to be exerted only in a direction at right angles 
with the line joining the nodes N and Ng, of the satellite's 
orbit. One of the effects, therefore, will be to wrench the 
orbit out of its position; that is, to change the position of 



OBJECTIONS FROM PLANETARY MOTIONS. 157 

the hinge-line N Ng on which it turns in suffering a change 
of inclination. Or, in astronomical language, the longi- 
tude of the ascending node N would be changed; and 
when once a motion from its primitive position should be 
begun, nothing but an exact equilibrating force would 
ever stop it. Thus the longitudes of the nodes of all the 
orbits of our system are changing their positions. A 
similar action would change the position of the apsides in 
reference to the nodes. 

(2.) I have already indicated (p. 120) another possible 
cause of such an irregularity, in the coalescence of the two 
or more spheroids into which a nebulous ring may have 
been separated. If the resultant planet, by the collision 
of these partial masses, has had its axis tilted over, its 
whole system of satellites must be correspondingly tilted. 

(3.) In discussing the direction and velocity of rotation 
acquired by a derived nebulous spheroid, I have pointed 
out the conditions under which certain relations of density, 
distance from the centre of the nebular mass, breadth of 
ring and velocity would result in retrograde motion. Such 
motion would be a normal phase in the earlier stages of 
the evolution of a nebula of a certain magnitude. It might 
seem, therefore, that no occasion exists for seeking further 
for the cause of retrograde motions in our system. But it 
must be borne in mind that the rotations in the Uranian 
and Neptunian systems are not completely retrograde, but 
lie in planes having high angles with the plane of the 
solar system. That of the Uranian system is, indeed, but 
little less than a right angle. But the cause here referred 
to would produce retrograde motion very nearly in the 
plane of the solar equator. For this reason I have not 
placed this explanation in the front. There is room to 
suppose that our solar nebula was not of such magnitude 
as to develop retrograde rotations in its earlier stages; and 
that the partial retrograde motions which we witness are 



158 ORIGIN OF THE SOLAR SYSXEM. 

due to the operation of some other cause. The condition 
of things seems very strongly to suggest the action of 
some overturning influence which might cease with any 
assiarnable decree of inclination. 

(4.) M. Faye, who accepts in its general features a 
nebular history for our solar system, has presented a 
modification of the theory of Laplace,* in which he 
expresses the opinion that retrograde motions would nor- 
mally prevail in the earlier stages of the evolution, and 
direct motions in the later. These views, as well as the 
similar ones of Professor Hinrichs, are cited on a previous 
page. It will be noticed, however, that their theories 
require the primitive retrograde motions to take place 
nearly in the common plane of the solar system. The 
same objection therefore rests against them as against the 
theory which connects direct rotations with increased 
density of the nebula. 

It may never become possible to demonstrate by which 
of the foregoing or other means a retrograde motion 
became established in the remoter parts of the system. 
However, unless our reasoning is entirely at fault, it 
appears that more than one possible means has existed for 
producing retrograde rotations in one part of the system, 
and direct rotations in another. The state of the facts is 
such, at least, that the existence of retrograde motions in 
the remoter regions cannot reasonably be assumed as a 
fatal or even a damao-ing- circumstance in nebular cosmol- 
ogy. 

2. The Periodic Times of the planets are lonxfer than 
the Kehidar Theory alloius.j — The periodic times are of 
course inversely proportional to the angular velocities; 
but, as before stated (p. 109) the angular velocities are 

* M. Faye, Comptes Rendus, xc, 637, March 22, 1880. 

t D, Trowbridge, Amer. Jour. Sci. II, xxxviii, 3, 4; Rev. W. B. Slaughter: 
The Modern Genesis, ch. v. 



OBJECTIOXS FROM PLANETARY MOTIONS. 159 

inversely proportional to the squares of the radii vectores. 
That is, the time of rotation of the nebulous spheroid 
would be proportional to the square of its equatorial 
radius. But, by Kepler's third law, the actual periodic 
times of the planets are proportional to the square roots 
of the cubes of their mean distances from the sun.* The 
periodic times of the planets are therefore greater than 
the theory allows. 

Now, I think it may be shown that such a lengthening 
of the periodic times is exactly what the theory requires. 

(1.) Let A, Figure 35, be the last formed planet at any 
epoch, revolving about the solar nebula in such an orbit 
and with such a period as would be required by the nebular 
theory. Let C D E represent the outer periphery of the 

* That is, while the nebular theory requires 

9 : 9' :: ?-'2 : r^ (p. 109), 
or what is equivalent, t : t' •.: r^ : r'^, 

the actual motions of the planets give, by Kepler's third law, 

3 3 

or t : t' :: r> : r'2' 

f and i' being the times of revolution of the nebulous disc in two different states 
of contraction, and therefore the theoretical periodic times of two planets result- 
ing from rings detached in those states, and r and ?'' the radius vector in the two 
states, or of the two corresponding planets. Now, if i' is less than t, then r' is 

less than r, and the ratio r^ : r'2 is greater than the ratio rs : r'a ; which 
means that i' when used for the periodic time of a i)lanet, is greater than i' when 
used to express the time of rotation of the nebulous spheroid when having a 
radius r'. Each planet, therefore, moves too slowly in reference to planets 
exterior to it. In other words, the progressive acceleration has been less than is 
required by the principle of equal areas. 

Professor Hinrichs has attempted to show analytically that the nebular 
theory involves a passage from the primitive velocity into the rate of motion 
expressed by Kepler's third law {Amer. Jour. Set. II, xxxix, 140-1). 

It is an error of some of the critics of the nebular theory to assume that the 
oblateness is proportional to the angular velocity, regardless of the value of the 
radius of rotation. Oblateness depends on centrifugal tendency, and this varies 
directly as the i)roduct of the equatorial radius of the spheroid into the square 
of the angular velocity, or, in other terms, directly as the square of the linear 
velocity and inversely as the equatorial radius. Rev. Mr. Slaughter in proving 
that the observed rotational velocity of Neptune is too small to have produced a 
ring-making degree of oblateness when the nebulous spheroid extended to 
Xoptunc, compares only angular velocities {The Neiv Genesis, 85-87). The 
same error is repeated in reference to the other planets. 



160 ORIGIX OF THE SOLAR SYSTEM. 

residual central mass at this time. Its centre of gravity 
being at S, the attraction of the whole mass constitutes 
the central force which determines the velocity of A in its 
orbit. In process of time another ring is detached, which 
gathers itself into another planet B or B'. The residual 
nebula is now shrunken in volume to the periphery F G H, 
and is diminished in mass by the whole amount of the 




Fig 35.— Pkocess of Lengthening the Periodic Tijie, and 
Acquiring an Elliptic Orbit. 

planet B. The mass B no longer constitutes a part of the 
mass whose attraction determines the velocity of A. The 
mass B, in certain situations accelerates that velocity, and 
in others, retards it. Its influence has become practically 
null. But now the diminished mass whose centre of 
gravity is at S exerts a diminished centripetal force on A. 



OBJECTIOKS FROM PLA:N'ETARY MOTIONS. 161 

The planet A, therefore, must recede from S, and move 
with diminished velocity in order that a diminished centrif- 
ugal force may still equilibrate the diminished centripetal 
force. It is perfectly obvious that the central mass which 
determines a certain velocity in a circum-rotating body, 
cannot determine an equal velocity when its mass is dimin- 
nished by the separation of another planet; and it is 
equally evident that the separated planet can contribute 
nothing permanently to the preservation of the former 
velocity of rotation. 

It must be remembered, however, that a resisting me- 
dium would neutralize a portion of the centrifugal tend- 
ency of the planet A, and thus slacken its motion without 
the necessity of a retreat from S. If there were no indi- 
cation that such retreat has taken place, we would be at 
liberty to assume that the loss of centrifugal force by 
ethereal resistance had been just equal to the loss of 
centripetal force by diminution of the mass S. But I 
think it will soon appear that these two influences were 
not equal. 

(2.) It seems probable that a most important influence 
was exerted upon the behavior of the spheroid by the 
enormous increase of density toward the centre. I have 
already directed attention in a general way to the neces- 
sary existence of such increase of density, but we are 
able to adduce the results of some calculations in reference 
to the density of the solar nebula.* If we assume that 
the oblateness of the spheroid remained nearly the same 
throughout the history of planet-making, and that in all 
its parts the centrifugal force was equal to the force of 
gravity, the following table will show the densities of the 
equatorial portions at the time of the disengagement of 
the several planetary rings: 

* D. Trowbridge, A?ner. Jour. Set., II, xxxviii, 353-4, Nov., 1864. 
11 



162 ORIGIK OF THE SOLAR SYSTEM. 

Mercury 27.10000000 

Venus 3.10700000 

Earth 1.00000000 

Mars 0,23440000 

Asteroids 0.01976000 

Jupiter 0.00311300 

Saturn 0.00037310 

Uranus 0.00003234 

Neptune 0.00001485 

The calculation shows that the density of the Mercurial 
ring was 1,825,000 times as great as the density at the 
outer periphery of the Neptunian ring.* As the disen- 
gagement of planetary rings continually diminished the 
nebular mass, it diminished the power of the central 
attraction to maintain its high primitive density or ten- 
sion, and we must therefore conclude that before the 
abandonment of the Neptunian ring the density at the 
distance of each of the future planets was greater than 
the above table shows. 

The same general conclusion is indicated by a calcu- 
lation of another sort, which shows that the radius of 
gyration of the solar nebula always bore a small ratio to 
the equatorial radius. In the following table the first 
column of numbers gives the length of the radius of 
gyration of the nebular spheroid at the time of sepa- 
ration of each of the planetary rings, and the second 
column gives the equatorial radius of the spheroid at 
the same epochs, assuming this to have been the same 
as the mean planetary distances at th,e present time. 

* It results from an investigation made by J. H. Lane on the necessary dens- 
ity of the sun's interior, on the supposition that it is composed of gases like 
hydrogen or atmospheric air, that such density at the interior must be of some 
value ranging from 7.11, about the density of cast iron, to 28.16, which is one- 
third greater than the density of platinum (J. H. Lane, Jjfier. Jour. Sci., 11, 1, 
63, 64). According to a law formulated by Legendrc and adopted by Laplace, 
the earth's density, which is 2.55 at the surface, is 8.5 at the mid-radius and 11.3 
at the centre. 



OBJECTION'S FROM PLANETARY MOTIONS. 163 

The mean distance of the earth is taken at 92^ millions of 
miles.* 

RADIUS OF GYRATION. EQUATORIAL RADIUS. 

Mercury 454,000 37,750,000 

Venus 725,600 66,750,000 

Earth 925,200 92,333,000 

Mars 1.269,000 141,000,000 

Asteroids 2,145,000 254,000,000 

Jupiter 3,187,000 480,000,000 

Saturn 5,022,000 881,000,000 

Uranus 8,480,000 1,771,000,000 

Neptune 11,870,000 2,775,000,000 

This table shows that the radius of gyration was always 
remarkably short compared with the equatorial radius of 
the spheroid. As the radius of gyration is the distance 
of the centre of inertia from the axis of rotation, it fol- 
lows that the greater portion of the mass of the nebula 
was always condensed about the centre. It is probable 
that when the Neptunian ring was abandoned, more than 
half the entire mass of the solar nebula was within the 
limits of the future orbit of the earth, and the greater 
part of this portion was within the future orbit of 
Mercury. 

To make the supposed facts clearly intelligible, let S, 
Figure 36, represent the centre of the nebulous spheroid 
at the time of the disengagement of the Neptunian ring, 
S N the equatorial radius, S K the radius of gyration, S M 
the radius of the future orbit of Mercury, and S E that 
of the earth. Now S K being represented by a quarter of 
an inch, S M is 3.2 times as great, S E, 7.7 times as great, 
and S N should be 23.4 times as great. That is, S N 
should be represented by 58^ inches. Or, if S N is repre- 
sented by six inches, S K should be one-fortieth of an inch. 

* Compare D. Trowbridge, Amer. Jour. Sci., II, xxxvii, 352-3; D. Kirkwood, 
Amer. Jour. Sci., II, xxxix, 6G-9; S. Alexander, Proc, Amer. .Issoc, Cincin- 
nati, 1851 (oral discussion only). 



164 



ORIGIN OF THE SOLAR SYSTEM. 



Now let us imagine the sphere whose 
radius is S N rotating about an axis 
passing through S. The point K is 
that at which, if an opposing force 
equal to the energy of rotation should 
be applied, it would completely arrest 
the rotation (supposing the spheroid 
rigid) without producing any ten- 
dency of the end S, of the radius, to 
move out of its place. Now, consid- 
ering that the point K is only one 
two hundred and thirty-fourth of the 
distance from S to N, we may easily 
imagine to what extent the mass of 
the matter must be gathered about 
the centre S. 

What then may be inferred from 
such relations of density ? It seems 
manifest that the exterior portions 
must contract much more rapidly 
than the interior. Their velocity 
would, therefore, tend to a more 
rapid acceleration. As the mass was 
not rigid, the exterior j^arts must 
have actually experienced a more 
rapid acceleration. Now, if an outer 
planet revolves with a greater veloc- 
ity in reference to the next interi'or, 
the ratio of their periodic times is 
brought nearer to a ratio of equality 
than before; and this is in the direc- 
tion toward the rate required by 
Kepler's third law; and we are per- 



FiG. 36. — Illustrating Increase of Density 
toward the centre of the nebulous 
Spheroid. 



OBJECTION'S FROM PLAN"ETARY MOTTON^S. 165 

fectly at liberty to assume tliat the cause here considered 
is the one which brought the periodic times to the relation 
expressed by that law.* 

But it may be further suggested, that if the central 
parts acquired most of their condensation before rotation 
began, they may be in a state of slower rotation than the 
more external parts. In tins case, the friction of the 
rapidly accelerating exterior portions upon the interior 
portion, would prevent the accelerating tendency from 
being fully realized, and thus the planetary rings, and the 
planets themselves, would have a slower orbital motion 
than would be indicated by the volume of the shrinkage, 
and might fall into conformity with Kepler's third law. 
Finally, each process of annulation removed from the 
spheroid its most rapidly rotating portion, and left only a 
slower rotating remainder. The sun, which remains, may 
be conceived as having undergone many thousand times 
less contraction since rotation began, than the matter 
about the equator of the primitive spheroid. f It is the 
remnant of an original nuclear portion, and has acquired 
but little more than its ancient density. Much of the in- 
crease of density due to cooling h*as been nullified by relief 

* Mr. D. Trowbridge expresses the opinion that " the angular velocity of the 
external parts would not be much Increased except by friction," and would thus 
tend to rotate according to Kepler's third law {Amer. Jour. Scl., II, xxxviii, 357) 
Since the internal parts have experienced more contraction than the external, it 
follows that their rotary velocity must have been increased more than that of the 
external, if the conde7isation took place after rotation had begun. In this case, 
Mr. Trowbridge's conclusion would be sound. But it seems very supposable 
tliat the generation of the rotation was a later event than the aggregation of the 
nebulous matter, and hence the condensation at the centre existed &<'/or« rrYa- 
tion began; and the development of that central density has not, therefore, 
accelerated the central rotation. 

t Eunis has conceived a more rapidly rotating exterior retarded by friction 
upon the interior as the explanation of the apparent discrepancy between tlieory 
and fact (J. Ennis, Origin of the Stars, chs. xvii, xix, and xxii). But he supposes 
tlie original rotation imparted only to the exterior by currents descending from 
higher to lower levels (p. 23.J), and supposes the interior to have acquired its 
rotation by friction with the exterior — though in some cases a general rotation 
may have been earlier generated by mutual collisions. 



166 ORIGIK OF THE SOLAR SYSTE^f. 

from the pressure of abandoned rings. In this view, the 
sun's present rotary velocit}^ might be nearly that which 
had been acquired at a very early period. It should, there- 
fore, be vastly less than the rate required by the simple 
laws of contraction. 

Similar reasoning in reference to the periods of Jupiter's 
satellites shows them to have been similarly retarded; but 
the retardation is only about one-fifth as much as in the 
case of the planets. This is what we should expect ac- 
cording to the nebular theory, since the mass of Jupiter is 
much less than that of the sun, and the difference in den- 
sity between the central and exterior portions would be less. 

From these two o-eneral courses of reasonino- it seems 
legitimate to conclude that the ratios of the periodic times 
of the planets resulting from an annulating nebula which 
began its rotation after condensation about the centre, 
must approach nearer a ratio of equality than they would 
if, as is generally assumed, the rotation of the nebula 
began before central condensation from gravity had been 
effected, and the velocities of rotation had been determined 
by the whole contraction. This diminished ratio of periodic 
times may result from an increased relative acceleration of 
external parts, or from a diminished acceleration of internal 
parts in acting on the external. 

Should it seem improbable that rotation began after 
condensation had taken place, it may readily be admitted 
that in the case of our solar nebula, and accordingly in 
other cases, an exceedingly slow rotation, existed before 
full condensation. In many cases the initial rotation 
would probably be extremely slow, both because generally 
the accessions of new matter would be relatively so small 
that their impact would possess little efficiency, and be- 
cause, striking, with equal probability, on all sides of the 
centre, their effects would tend to neutralize each other. 
It will be borne in mind also, that in aggregations as inco- 



OBJECTIONS FROM PLANETARY MOTIONS. 167 

herent as nebul[e, collisions would develop vastly less 
rotary effects tlmn collisions between solid bodies. 

3. The Periodic Times of tJie planets we shorter than 
the Nebtdar Theory alloics.^ — It is claimed that the princi- 
ple of conservation of areas would give the spheroid at 
the orbit of Mercury a period of rotation equal to about 
eighteen hundred of Mercury's years; so that Mercury 
when detached from the sun must have had about eighteen 
hundred times smaller a quantity of motion than at present. 
This result is reached by taking the sun's actual rotation 
period as a starting point, and calculating from what Mer- 
curial velocity it must have resulted on the principle of 
equal areas. f But this mode of calculation is wholly falla- 
cious, since we have abundant reason for believing, as 
already explained, that the sun's actual rotation has not 
resulted simply in accordance with the law of equal areas 
in a contracting homogeneous medium. Investigators of 
this subject generally admit that the sun's acceleration 
of rotation has been diminished. Moreover, the great 
central condensation of the primitive nebula prevented 
contraction and acceleration in the same ratio as was ex- 
perienced by the remoter and more tenuous zones. The 
result of the comparison between Mercury's actual veloci- 
ty and that which he must have had on the principle of 
equal areas, calculating back from the sun, is precisely 
what the progress of the nebular evolution would require; 

* Rev. S. Parsons, Meth. Quar. Rev., Jan., 1877, p. 151. 

tLet R— radius of sun; r = radius of nebula when expanded to Mercury's 
orbit; 0'= angular velocity of tiie sun, and = angular velocity when expanded 
to Mercury's orbit. Then by the principle of equal areas, 

0:6':: R'2 :r^: .-. 6» = 6'—. Also 0'=e~r. 

But 0'=O°.59 per hour; 7? = 430,000 miles; r := 35,750,000 miles; therefore, 

B = 0°. 00008536 per hour. But Mercury's actual angular velocity is = 

87.97 X 24 

0°.1705 per hour. Hence his actual angular velocity is "^^^'^^^ = 1998 times as 

rapid as it should be on the principle of equal areas. 



168 ORIGIN OF THE SOLAR SYSTEM. 

and tends to confirm the nebular theory instead of weak- 
ening it. 

It would be quite as legitimate to assume Mercury's 
period as a starting point and inquire what must have 
been the sun's angular velocity. This would show that 
the sun's velocity is 1998 times too slow. But this under- 
rate of the sun's rotation is quite in accordance with our 
reasoning. 

This objection is substantially the same as the last. In 
that it is maintained that the orbital velocity of each 
planet is too slow in relation to planets exterior to it. 
Here it is maintained that a planet's orbital velocity is 
too rapid in reference to a planet interior to it. The two 
propositions are convertible. 

4. The Periodic Time of Phohos, the inner satellite of 
Mars, is too short. — ^i. Faye, in the first of his important 
memoirs on nebular cosmogony,* has presented it as a 
difficulty in the theory of Laplace that the inner satellite 
of Mars revolves in about one-third the period of the 
planet's rotation on its axis. "The period of rotation of a 
planet, said Laplace, must be, according to my hypothe- 
sis, less than the period of revolution of the nearest body 
which circulates around it. * * * Nor is this the 
sole exception to the theorem of Laplace. The same is 
true of a part of the rings of Saturn, as was observed 
some time since by M. Roche. There must exist, therefore, 
some defect in the mother idea of the theory." 

Undoubtedly the Laplacean conception of nebular cos- 
mogony must be somewhat modified. Many facts brought 
to light within the last three-quarters of a century are now 

* M. Faye, Comptes Bendus, torn, xc, 5G9, March 15, 1880, Prof. C. A. Young 
also, in a lecture delivered :n New York in January, I880, speaking of the theory of 
Laplace, is reported to have said, '• Whether this system can be true in its entirety 
I very much doubt. It is necessary to suppose some change in its mode of action; 
for otherwise the moons of Mars never could revolve quicker than the rotation 
of the planet itself. Yet something like this may be the correct theory." 



OB.TEOTIOXS FROM PLANETARY MOTION'S. 169 

available as a basis for reasoning, and it is necessary to 
modify some of the details of his theory. Laplace rea- 
soned on the assumption of an absolute void in the inter- 
planetary spaces, and he obtained only a first glimpse of 
the influence of tides upon the rotation-period of a planet 
or satellite. We now understand that the spaces around 
us are thickly occupied by particles of matter which I 
have designated " cosmical dust." We believe generally, 
in the existence of a material " ether." The mathematical 
theory of tidal action has very recently been followed out 
in its remote consequences to such an extent as to unfold 
new and surprising cosmical effects in the primitive and 
ultimate stages of planetary life. 

I have already pointed out the necessary influence of 
the storm of meteoroids in transforming the energy of 
orbital motion in any planetary body, but especially in 
bodies as small as the Martial satellites. It is entirely 
credible that the satellites of Mars, and especially the 
inner and smaller satellite, should by such means, have 
been drawn nearer the centre of their motions, and thus 
accelerated in orbital velocity. When Phobos was 12,480 
miles distant from the centre of Mars, its period of revo- 
lution was three times its present period. It then verj'- 
nearly equalled the day of Mars, and was just two-thirds 
the period of the outer satellite, Deimos.* 

But it is manifest that an ulterior result of solar tidal 
action upon any planet whose rotation has become syn- 
chronous with that of its dominant satellite (whether by 
acceleration of the satellite or retardation of the planet) 

*Tlie relation between distances and times is given by Kepler's third law 
from which 

t:t'::r'^ : V' and^'=/(^)^. 

To find at what distance a satellite will perform its revolution in a period n 

-)^. From this r'=?ir, and in the case of 

Phobos, r'=33X6,000=12,480. 



170 ORiGi>;r OF the solar system. 

will be a further retardation of the planetary rotation, so 
that the day will become longer than the lunar month, as 
in the case of Mars and Phobos. It is at least conceivable, 
on physical principles, that the relation of the motions of 
these two bodies is an incident of the old age of the 
Martial system. 

5. We have no adequate cause assigned for the inaug- 
uration of a Rotary Motion.\ — I believe the considera- 
tions heretofore presented (pp. 94-106) must convince any 
unbiased mind that the chances of the causation of rotary 
motion are nearly as infinity to unity. It may be well, 
however, to correct a misapprehension which has been 
used against the theorem that attraction from without 
would inaugurate rotation. Mr. Parsons says, in effect, 
that such attraction would, indeed, initiate rotation about 
the shortest axis; but the prolateness caused would be 
directed constantly toward the attracting body, and would, 
like a great tide, promptly arrest the rotation which had 
been begun. But, as all nebula? must experience a mo- 
tion of translation, this attracting body unless moving in 
the line of the prolate axis, would finally deflect this axis, 
and as the body should pass to such distance that the com- 
parative influence should be null, the prolate nebula would 
cease to be prolate, and would be left in the process of a 
slow rotation. Or if, while the attracting body remains 
in the neighborhood, a third body should pass through 
such a position as to influence one extremity of the pro- 
late axis more than the other, this influence might be 
sufficient to overcome the fixity caused by the first attract- 
ing body. But, it will be recalled by the reader that the 
most plausible conception of the forming process of nebula? 
represents them as falling together and acquiring of neces- 
sity a rotary motion from an early stage of their existence. 

tRev. S. Parsons, Methodigf Quarterly Review, January, 1877, 144-5; Rev. 
W. B. Slaughter: The Modern Genesis, ch. iii. 



OBJECTIONS FROM PLANETARY POSITIONS. 171 

§ 3. OBJECTIONS BASED ON RELATIONS OF PLANETARY 
POSITIONS. 

1. The inclinations of the planetary orbits to the plane 
of the sitn\^ equator* — It is sometimes pretended that all 
the primary and secondary orbits should be strictly coinci- 
dent; and it is at once evident that by the theory, they nfiust 
have been so, if the system had assumed form in the 
absence of all perturbating i7ifluences from loithout. This 
is the unconditional and unwarranted assumption of the 
objectors. But we know, in the first place, that pertur- 
bating- influences could not have been absent. The grave 
misapprehension exists in some minds that the nebular 
theory assumes a complete evolution through the action of 
its own internal forces alone. Rev. W. B. Slaughter em- 
ploys the following language: "We must not forget that 
this cosmical sphere is revolving in a void. There is no 
external matter whose friction or attraction can modify 
the result. If it be alleged that there is other matter in 
the universe whose attraction must have reached the cos- 
mical sphere and affected it, we reply that the nebular 
hypothesis does not take such external attractions into 
account. \ It professes to find all its world-forming forces 
within the mass." \ This is a profound and fatal miscon- 
ception, but one which is made the basis of much of Mr. 
Slaughter's criticism. In fact the system of Neptune is 
so far removed that we may say it feels but slightly the 
controlling influence of the sun, while the stellar masses 
must exert an influence somewhat perceptible. A similar 
remark may be made in reference to Uranus and Saturn. 
Moreover when one planetary orbit should have been 
thrown out of coincidence with the plane of the solar 

*Rev. W. B. Slaughter: The Modern Genesis, ch. vi. 

t It is a >fufficieiit reply to this to refer the reader to the nebular theories of 
Kant and Laplace presented in part IV, chap, ii and iv. 
X The Modern Genesis, 68, 69. 



172 ORIGII!^ OF THE SOLAR SYSTEM. 

equator, it would act on all the other planets to producq 
the same kind of disturbance. That the inclinations in 
question are affected by the mutual attractions of the 
planets is a well settled principle in cosmical physics; and 
nothing- is more supposable than that the whole value of 
the inclinations has been created by these or kindred 
causes. Sir Isaac Newton says: " While comets move in 
very eccentric orbits in all manner of positions, blind fate 
could never make all the planets move in one and the 
same way in orbits concentric, some irregularities excepted 
which may have risen from the mutual actions of comets 
and planets upon each other, and which will be apt to 
increase till this system wants a reformation." * How- 
ever, in spite of Newton's apprehension, we now know, 
from the progress of the recognized oscillations in these 
planes,t it is ascertainable that in the course of time they 
return nearly to the positions from which theory supposes 
them to have started. Thus it appears that Mercury will 
sometimes coincide with the plane of the sun's equator; 
Venus will approach within 5° 25'; the earth within 3°; 
Mars, within 10°; Jupiter, within 5°; Saturn, within 5° 5'; 
Uranus, within 5°, and Neptune within 5° 8'. Similarly, 
the plane of the moon's orbit will approach to within 18° 
of coincidence with the plane of the earth's orbit. The 
proper plane of reference, however, for these inclinations 
is not the ecliptic, which is only the position in which the 
ever-changing plane of the earth's orbit happens to lie at 
the present time, but the "invariable plane of the solar 
system." With this the planets make only the angles 
indicated thus: Merciiry, G° 20' 58"; Venus, 2° 11' 14" 
Earth, 1° 35' 19"; Mars, 1° 40' 44"; Jupiter, 0° 20' 
Saturn, 0° 55' 31"; Uranus, 1° 1' 45" ; Neptune, 0° 43 
25". In the course of time these inclinations will reach 

* Newton : Optics, p. 376. 

t See Stockwell, Smithsonian Contributions to Knowledge, xviii. 



OBJECTIONS FROM PLANETARY POSITIONS. 173 

the following minima: Mercury, 4° 44' 27"; Venus, 0° 0' 
0"; Earth, 0° 0' 0"; Mars, 0° 0' 0"; Jupiter, 0° 20'; Sat- 
urn, 0° 47' 16"; Uranus, 0° 54' 25"; Neptune, 0° 33' 
43".* Now it would seem that instead of any material 
conflict with the theory in this state of facts, we discover 
an impressive confirmation of it. 

2. The Breadth of Intervals hetioeen the planetary 
orbits is not clearly explained on the nebular theory. \ — It 
has been suggested that instead of a periodic disengage- 
ment of a ring of considerable mass, the equatorial peri- 
phery would continuously flatten out into a continuous 
disc-like expansion; so that nearly the whole nebulous 
mass would ultimately assume a discoid or flatly lenticular 
form, when annulation and planetation would take place 
in all the rings simultaneously. Under this view the rings 
should be more numerous, or at least more approximated 
to each other. I have given this subject considerable 
study, and have reached the conclusion that the original 
opinion of Laplace is the more probable one. I have 
attempted to show \ that the act of annulation would be 
periodic, and the reader is referred to the statements 
already made.§ The intervals between the planetary orb- 
its, therefore, instead of conflicting with the nebular 
theory, ought to be cited as confirmation. 

It might be said further, that the various inclina- 
tions of the planes of the planetary orbits is a circum- 
stance less likely to result from a simultaneous origin of 
the planets than from successive origins. 

3. Tlie 'nebular theory does not account for the Elliptic 
Forms of the planetary Orbits. — The equatorial periphery 

* J. N. Stockwcll, Smilhsordan Coutribulions, xviii, Doc. 232, pp. 166, 169. 

t Newcomb: Popular Astronomy^ 497-8. Tliis is not presented by Professor 
Newcomb as a fatal ditficiilty, but is only alleged against a non-essential feature 
of the Laplaeean hypothesis. 

tPartI, Chap, ii, §3, 3. 

§ Ilinrichs concludes that the process of annulation would be periodic, and 
that the intervals would be equal {Amer. Jour. Sci.^ II, xxxix, 140 1, 144-7). 



174 ORIGIX OF THE SOLAR SYSTEM. 

of the rotating nebula must have been at all times nearly 
circular. This would result in a circular ring and a circu- 
lar orbit for the planet. Let us examine the point. 

(1.) I have stated above (p. 160) that a reduction of the 
central mass S, Figure 35, would cause the planet to 
retreat. It is scarcely supposable that a motion away 
from S would be inaugurated without carr3'ing the planetj 
by virtue of its inertia, beyond the point of equilibrium 
between centrifugal and centripetal forces. Brought to a 
halt at a point beyond this equilibrium, it would be in the 
position of a body let fall toward S, but actuated at the 
same time by a strong transverse impulse. I have already 
explained (p. G7) that under such circumstances the planet 
would describe an elliptic path around the centre of 
attraction. 

It is not necessary to conceive the planet as retreating 
with the suddenness indicated by the dotted line A c. The 
result would be the same whatever number of revolutions 
it might make in reaching its remotest point. 

If these views are correct, the amount of a planet's 
eccentricity, other things being equal, should be propor- 
tional to the mass of the planet next interior. Saturn, 
with the planet Jupiter next interior, should have a 
greater eccentricity than Uranus with the mass of Saturn 
next interior. Accordingly the eccentricity of Saturn is 
.056, while that of Uranus is .046. So the eccentricity of 
Mars should be greater than that of tlie earth. In fact 
the eccentricity of Mars is .093, while that of the earth is 
.017. So the eccentricity of the earth,. 017, as determined 
by the withdrawal of Venus, is greater than that of 
Venus, .007, as determined by the withdrawal of the 
smaller planet Mercury. The eccentricity of Mercury is 
.206 with no interior planet certainly known to have 
caused it. Until a considerable interior mass is demon- 
strated, it is allowable to attribute this comparatively 



OBJECTION'S FROM PLANETARY MASSES, ETC. 175 

large eccentricity to the proximity of Mercury to the 
perihelia of cometary and other erratic bodies drawn 
toward the sun. Most of the asteroids have large eccen- 
tricities; but these may be attributed chiefly to the influ- 
ence of neighboring planets, especially of Jupiter. The 
small masses of Mercury and the asteroids would, of 
course, render them specially susceptible to perturbative 
influences. 

(2.) The circular orbit is one of unstable equilibrium 
in the actual universe. It is impossible of conservation. 
Every external attraction to which the planet might be 
subjected would pull it from its path. 

Suppose a planet revolving in a circular orbit, the per- 
turbative influence of any attractive body, as, for instance, 
a neighboring planet, would draw it from a circular path; 
and as that influence should again diminish, the planet 
would swing toward its circular orbit again. But it would 
swing too far. By the laws of mechanics we know that its 
orbit would henceforth be elliptic. It is shown as the 
result of the most elaborate calculations, that the eccen- 
tricity of each planetary orbit is actually affected by the 
attraction of each sister planet; and the value of the 
eccentricity increases and diminishes according as the 
resultant perturbation increases or diminishes in amount. 
Beyond all question this cause must convert an original 
circular orbit into an elliptic one. 

§ 4. OBJECTIONS BASED ON RELATIONS OP PLANETARY 
MASSES AND DENSITIES. 

1 . The 7nass of the Asteroids is smaller than the nebular 
theory requires. — All the asteroids known aggregate less 
than i-^-^-Q the bulk of the earth, and their mass probably 
is much less in proportion. Leverrier calculated that the 
greatest possible mass of all the asteroids, discovered and 
undiscovered, could not exceed one-fourth of the earth's 



176 oriCtIX of the solar system. 

mass. Such an asteroidal mass would explain the secular 
motion of the perihelion of Mars. But a revised determina- 
tion of the earth's mass shows that the earth's influence is 
almost sufficient to account for this secular motion; and 
hence the total asteroidal mass must be exceedingly small. 
But I am not aware that the nebular theory necessitates 
any direct simple relation between the masses of the 
planets in a system, though it is true that the mass of each 
planet is connected with its period of revolution and mean 
distance from the body around which it revolves. It is 
also true that in general we should expect the remoter 
planets to possess larger masses because formed from rings 
having larger circumferences. This is generally the case, 
and is so far a confirmatory circumstance. But the theory 
carried out in the midst of space already populated by 
numberless moving bodies does not forbid the disengage- 
ment of rings of small mass. The asteroidal and the 
Martial masses may both have been originally less than 
the principle of regular gradation permits. But it may 
also be suggested that both these masses may have been 
reduced from their original amounts by precipitation of 
portions into the solar nebula before the latter had 
shrunken sufficiently within the perihelion positions of 
these masses.* 

2. The Disrupted State of the asteroidal onass is an 
Anomaly in the operation of the theory. — The circumstance 
is extraordinary, but not anomalous. The Saturnian rings 
are extraordinary, but so far from anomalous that they 
bring strong testimony to the soundness of the theory. 

(1.) I have heretofore (p. 119) suggested the probability 
of the stratification of the nebulous rings. This suggestion 
seems to have occurred to Laplace. Now, with the dis- 
ruption of a stratified ring, it is quite conceivable that 
numerous planets might result, while it is equally con- 

* As suggested by D. Kirkwood, Amer. Jour. Sci., Ill, i, 71. 



OBJECTIONS FROM PLAKETARY MASSES, ETC. 177 

ceivable that they might coalesce into one. Either con- 
tingency is entirely within the provisions of the theory. 

(2.) Moreover, it was a suggestion of the late Professor 
Benjamin Peirce that an intra-Jovian ring might have 
persisted until excess of perturbation and consequent 
oscillation "brought it into contact with the planet Mars, 
by which collision it was broken into asteroids.* 

(3.) Finally, Professor Clerk-Maxwell in investigating 
the conditions of equilibrium of Saturn's rings, f reached 
the conclusion that undulations in a fluid ring, under 
certain circumstances, would result in breaking up the 
ring into small satellites. Mr. Trowbridge has applied 
this conclusion to a ring persisting between Mars and 
Jupiter until it had attained the condition of an incom- 
pressible fluid, when it would, at a later period, be broken 
into a multitude of asteroids. 

The possibilities of the nebular theory therefore deprive 
of all force any objection based on the existence of a 
group of asteroids.:}: 

3. The densities of the outer planets are so loio that if 
composed of the same materials as the earth they should 
he of a temperature sufficiently high to he self luminous. % 
— All recent observations lead toward the opinion that these 
planets are enveloped in a thick mantle of aqueous vapors/ 
It is only the exterior of this envelope which is exposed 
to our view. On planets of such mass, the density and 

* B. Peirce, Gould's Astronomical Journal, ii, 18; also Annual of Scientific 
Discovej'y, 1852, 3T9. Compare G. Hinrichs, Amer. Jour. Sci., II, xxxix, 54. 

t Clerk-Maxwell: On the Stability of the Motions of Saturn's Rings, 1856. 

X Mr. Herbert Spencer adheres to Giber's theory of an exploded planet, and 
sets forth the grotesque conception of a planet liquefying and even solidifying 
around a gaseous nucleus, the tension of wiiich finally. overcomes the strength 
of the shell (Spencer, Westminster Review, Ixx, 123, July, 1858; Essays, Scientific, 
Political and Speculative, second series, New York, 1864). Other suggestions in 
this essay must be regarded as entirely an evolution from inner consciousness, 
among which that of hoop-shaped rings is sufficiently extraordinary and gratui- 
tous. 

I Rev. W. B. Slaughter: The 31oderii Genesis, ch. xiii. 
12 



178 ORIGIN OF THE SOLAR SYSTEM. 

perhaps the vapor-beariiig height of the atmosphere must 
be many times greater than on the earth. By all this 
amount then, the diameter of the aqueous envelope ex- 
ceeds that of the planetary body. Our exaggerated esti- 
mate of the diameter of the planet results in an underesti- 
mate of its density. After making all corrections, and 
admitting that Jupiter is still in a heated condition, it does 
not appear that the densities of the outer planets are at 
all different from what the nebular theory requires; since 
that demands progressive increase in density toward the 
centre. (But see Chap, iii, §§ 5 and 6, and Chap, iv, § 5.) 

A fundamental fallacy, which develops itself in many 
other forms, is the assumption that the nebulous spheroid 
proceeded to increase in density precisely in proportion to 
its diminution in volume, and that the rate of contraction 
must be exactly in the inverse ratio of the mass. The 
contraction is proportioned to the loss of heat in the 
whole mass. The power of radiation is proportioned to 
the surface; and the loss of heat is in the same proportion, 
provided the temperature of the lohole mass dbninishes 
equally. But the surface is proportional to the square of 
the radius, while the mass, when the density is uniform, 
is proportional to the cube of the radius. In other words, 
the surface diminishes more slowly than the mass; so that 
the rate of radiation diminishes less rapidly than the mass 
even when the whole mass cools uniformly. But no 
large mass can cool with complete uniformity; and in a 
mass which has become solid on the exterior or through- 
out, "SO as to prevent convection of heat by free mobility 
of the particles, the rate of cooling will be also retarded 
by the process of conduction from the interior to the sur- 
face. Hence every planetary mass must proceed at a con- 
tinually retarded rate of cooling. 

For these reasons no two planets of the same mass can 
have attained to temperatures proportioned to their ages. 



objectio:n^ from terrestrial duration. 179 

The temperature is a function of the age, but not a simple 
function of it. Nor can two planets of the same age but 
of different masses have attained to thermal conditions 
proportional to the masses. Nor, if the thermal condi- 
tions were the same, would their densities be the same. 
Density depends on thermal conditions and on mass. 
Hence all the captious criticisms on the nebular theory 
based on supposed non-conformities of the planetary densi- 
ties are founded on misapprehension of the physical con- 
ditions involved. 

§ 5. OBJECTION BASED ON RELATION TO TERRESTRIAL 
DURATION. 

Tlie nebular theory does not admit as great an Age for 
the World as geology requires.^ — Sir William Thomson, on 
the basis of the observed principles of cooling, concludes 
that not more than ten million years can have elapsed 
since the temperature of the earth was sufficiently reduced 
to sustain vegetable life;f and on the duration of tidal 
action reaches a similar result. | Helmholtz calculates that 
twenty million years would suffice for the original nebula 
to condense to the present dimensions of the sun. Pro- 
fessor S. Newcomb requires only ten million years to 
attain a temperature of 212" Fahr.§ Croll estimates seventy 
million years I for the diffusion of the heat which would 
be produced by the collision of two such nebulae as would 
constitute the primitive nebula postulated by the theory. 
But meantime Bischof calculates that 350 million years 
would be required for the earth to cool from a temperature 

*Rev. S. Parsons, Meth. Qiiar. Rev., Jan., 1877, pp. 142-3. 

t Thomson and Tait: Natural Philosophy, Appendix D, also §§ 882. 833, 834, 
847, 848 (but 847-9 cancelled in Glasgow address) ; Trans. Roy. Soc. Edinb., xxiii, 
pt. I, 157, 1802. 

X Thomson, Trans. Geol. Soc, Glasgow, iii, 1. 

§ Newcomb: Popidar Astronomy, 509. 

II Croll : Climate and Tune, 335, 



180 ORIGIX OF THE SOLAR SYSTEM. 

of 2,000° to 200° centigrade. Reade, basing his estimate 
on observed rates of denudation, demands 500 million 
years since sedimentation began in Europe.* Lyell ven- 
tured a rough guess of 240 million years; Darwin thought 
300 million years demanded by the organic transformations 
which his theory contemplates; and Huxley is disposed to 
demand a thousand millions. *'Here," says Mr. Parsons, 
"is a clear conflict between the naturalist and philosopher. 
Either the geologist must be compelled to surrender some 
hundreds of millions of time, or the physicist must give 
up the nebular theory as the foundation of the condensa- 
tion hypothesis of the sun's heat and the earth's present 
temperature. The geologist will probably carry the day, 
and the nebular hypothesis will have to give way to some 
other speculation relative to the origin of the solar system." 
A better considered view of this diversity of estimates 
seems to me to be the following: Some biologists, im- 
pressed by the slowness of organic transformations, seem 
to close their eyes tight and leap at one bound into the 
ab^'ss of millions of years, of which they have no more 
adequate estimate than of infinity. They have a sort of 
impression that some hundreds of millions would not be 
too much. They are destitute of the first exact chrono- 
logical datum from which to set out. Similarly, certain 
physical geologists having roughlj' estimated the rate at 
which erosion is going on, make this best attainable 
knowledge the basis of a provisional calculation of the 
time required for all the erosion which tb.ey suppose to 
have taken place. Manifestl}^, the result involves too 
many guesses and estimates and best judgments to be of 
any value in subverting the significance of the uniformities 
of the solar system and the starry heavens. Lastly, the 
physicists have proceeded from more exact data, and by 
more exact methods, to results embracing fewer unascer- 

*Reade, Address Liverpool Geol. Soc, 1876. 



OBJECTIONS FROM COMETS, STARS AKD NEBULA. 181 

tained elements and fewer assumptions than in either of 
the other cases. The shorter periods are, therefore, far 
most likely to represent the truth; and these are derived 
according to the principles of the nebular theory. 

I shall hereafter show that physical science places the 
geologist in possession of facts which enable him, without 
receding from his best methods of calculation, to deduce 
a value for the age of the world, which lies quite within 
the limits fixed by physical investigation. The great fact 
to which I allude is the enormous exaggeration of the 
forces of sedimentation in the world's early history, due to 
the enormous development of tidal action at a time when 
the lunar mass was much nearer the earth than at present, 
/^he conflict, therefore, between the physicists and the 
geologists is entirely imaginary. Even if it were real, it 
would be no more than a conflict between vague opinion 
and the results of calculations which themselves embody 
many data which are merely assumed. 

§ 6. OBJECTIONS BASED ON RELATIONS OP COMETS, 
STARS AND NEBULA. 

1. Cometary phenomena ought to be provided for 
binder the nebular theory^ but this is imj^ossible* — This 

*Rev. S. Parsons, Methodist Quarterly Heview, January, 1877, pp. 132-4. 
Compare the views of D. Kirkwood, American Journal of Science, II, xxxviii, 
16-18, who thinks a majority of the periodic comets have originated in the sys- 
tem, and says Faye's comet " may be regarded as a connecting link between 
planets and comets." Mr. Herbert Spencer, also, has undertaken to show that 
many more comets approach our sun from the direction of the poles of the ecliptic 
than from the direction of its plane; and hence indicate a physical connection 
with our system {Westminster Review, Ixx, 110-12, July, 1858). He thinks comets 
to be mere detached flocculi left behind during the contraction of the solar nebula. 
Much information in reference to comets and their connection with meteoric 
matter has been gained since Mr. Spencer wrote, and his suggestion does not 
seem as plausible as it did. Moreover, if comets have chiefly originated within 
the sphere of attraction of our system, it is improbable that so many of them 
should have acquired hyperbolic orbits which carry them indefinitely beyond 
the controlling influence of our sun. Nor does it seem credible that after time 
enough has elapsed to form and consolidate so many planets, those cometary 



182 ORIGrN OF THE SOLAR SYSTEM. 

pretence is totally inadmissible. Only two reasons have 
been presented on which it can be based: (1.) Some of 
the comets have eccentricities but little greater than those 
of a few of the asteroids, and thus a gradation exists from 
the planetary orbit nearly circular to the cometary orbit 
with extreme eccentricity. (2.) That a physical connec- 
tion actually exists between the comets and planets is 
shown by the coincidences between the aphelia of groups 
of comets and the mean distances of certain planets, espe- 
cially the four outer ones. 

Now, the objections to this claim, in addition to the 
suggestions thrown into a note, are the following: 

(1.) Neither Laplace nor any subsequent astronomer has 
been impressed by any such relations between the comets 
and planets as to suggest that they belong to the same sys- 
tem, or have had a common history. Laplace says: " In our 
hypothesis the comets are strangers to the planetary sys- 
tem. In regarding them, as we have done, as small nebu- 
la wandering from solar system to solar system, and 
formed by the condensation of nebulous matter spread 
v^^ith such profusion through the universe, it is apparent 
that when they arrive in that part of space where the 
attraction of the sun is predominant, he forces them to 
describe elliptic or hyperbolic orbits. But their movements 

flocculi should be just arriving; nor, if just arriving, should they be seen mov- 
ing with velocities which would carry them across the diameter of our system in 
a few years and across the sphere of our sun's attraction in a few centuries. As 
to Mr. Spencers first assumption, the facts of the case have been collated by 
Lamont, and stand as follows: Of comets having an inclination to the ecliptic 
ranging from 0° to 30°, 24 have direct motion and 15 retrograde. Of those from 
30° to 60°, 34 have direct motion and 42 retrograde. Of tliose from 60° to 90°, 
27 have direct and 29 retrograde motion. Thus, their inclinations are somewhat 
equally distributed from the equator to the pole. At the same time, we notice 
the concurrent fact that eighty-five of these comets have direct motion and 86 
retrograde.— Lamont : Astronomie und Ei-dmagnetismus, Stuttgart, 4L 

M. Faye also records the opinion that the comets belong to our system, and 
in the modified nebular theory which he has advanced, attempts to show how 
their eccentric movements might have originated {Comptes Bendus, tome xc, 
pp. 640-2). 



OBJECTIONS FROM COMETS, STARS AND NEBUL.^. 183 

being equally possible in all directions, they should move 
indifferently in all directions, and with all inclinations to 
the ecliptic, a demand which conforms to what we observe. 
Thus the condensation of nebulous matter by which we 
proceed to explain the movements of rotation and revolu- 
tion of the planets and satellites in the same direction, 
and in nearly the same plane, explains equally why the 
movements of the comets depart from this general law." * 

(2.) It signifies nothing if, out of hundreds of comets 
which have been recorded, we are able to select a few 
with small eccentricity. The very theory which we main- 
tain in reference to the origin of the comets requires that 
some of them should have direct motion and a minimum 
of cometary eccentricity. But it also implies that among 
the whole number of comets, retrograde motion should be 
nearly as common as direct motion, and that many of the 
cometary orbits should be ellipses of extreme eccentricity, 
or even parabolic or hyperbolic — all according to actual 
observation. The objector is not at liberty to employ cer- 
tain exceptional characteristics of a group of phenomena 
in determining upon a classification; he is bound to take 
account of the entire assemblage of characters. This 
principle of reasoning is so elementary that one can hardly 
account for its disregard except through a spirit of cap- 
tious criticism. 

(3.) A physical connection certainly exists between the 
comets and the planets, and the two classes could not co- 
exist in the presence of each other without manifesting it; 
but this does not imply that such interaction has always 
existed, or that the two classes of bodies have had a com- 
mon history. Introduce any other strange body into 
the system, and the same kind of physical connection 
would be immediately established. It is generally under- 
stood that a cometary body entering the system is \^ry 

Laplace : Systhne du Monde, ed. 1824, p. 414. 



184 0riCtI:n^ of the solar system. 

likely to be so attracted by some one of the planets that a 
new career and a new pathway must date from the time 
and place of such disturbance. A comet starting on a 
new career from the orbit of Jupiter might thenceforward 
move in an elliptic orbit having its aphelion at about the 
distance of Jupiter from the sun. 

2. The requisite Tenuity of the assumed nebula injill- 
ing the orhit of Neptune loould result in its Dissipation 
into infinite space.^ — Since, under standard conditions of 
pressure and temperature at the earth's surface, the mole- 
cules of hydrogen have a motion among themselves of an 
average velocity of 6,000 feet per second, and those of 
oxygen 1,800 feet, and those of air 1,400 feet per second, 
these velocities would be so increased in the supposed 
nebula that the molecules would fly off into space. It is 
calculated that at a freezing temperature the motion of 
hydrogen atoms would be 9,000 feet per second, while a 
velocity of 520 feet per second would be sufficient to 
overcome the restraining force of gravity. Still more 
would this be the case if the nebula were intensely heated. 

I do not conceive it necessary to discuss the merits of 
a speculation, one of the consequences of which is to 
negate the existence of something which stands revealed 
to the ocular sense. The speculation concludes that a 
nebula sufficiently tenuous could not exist, and here it is 
existing before our eyes. What are those faint films 
described by Sir William" Herschel as barely discernible 
in his great telescope and spreading over several square 
degrees of space ? f What is the nature of the zodiacal 
light? What is the tenuity of the tails or even the 
comae of comets, through thousands of miles of which 
faint starlight is able to pierce, and which are so unsub- 
stantial that the entire cometary collection — nucleus, coma 

*Rev. S. Parsons, Meih. Quar. Rev., Jan.. 1877, pp. 141-2. 

t Herscbel, On nebulous stars, properly so-called, Phil. Trans., 1791. 



OBJECTIONS FROM COMETS, STAKS AND NEBULA. 185 

and tail — is unable to disturb perceptibly the movements 
of bodies as small as Jupiter's satellites? If these are 
not examples of matter sufficiently tenuous, which, not- 
withstanding' their tenuity, are held together by the 
attraction of their parts, we should inquire what adequate 
warrant exists for the assumption that material molecules 
possess the power of continuous motion in one direction 
rather than a vibrating motion. And whether their mo- 
tion is not instituted and limited by the immediate neigh- 
borhood of other molecules. And whether it is not 
conceivable that molecular attraction would restrain neigh- 
boring molecules from flying off an indefinite distance. 
And whether, finally, the objector has ascertained what 
degree of tenuity would so separate molecules or atoms 
that each in its motion should fail to strike another atom 
or molecule and be turned back by it. 

But another point is overlooked by the objector. When 
it is calculated that the matter of the solar system uni- 
formly distributed through a sphere having a diameter 
equal to Neptune's orbit, would possess a certain extreme 
degree of tenuity, this is merely a calculation. It may 
serve to give us a conception of the vastness of the space, 
but does not teach us anything respecting the actual 
tenuity or condition of nebulous matter. The tail of a 
comet is not a continuous gas. The matter of the zodi- 
acal light is composed of discrete, solid particles. The 
nebulous rings of Saturn are not a continuous gas. Our 
conception of the crude condition of nebular matter views 
it as a cloud of floating masses and particles more or less 
dissociated, but tending slowly toward aggregation. Tens 
and hundreds of miles may intervene in some places. 
Each has its own motion in addition to the general mo- 
tion of the cloud; and hence collisions frequently occur. 
If any aeriform matters exist, or are brought into exist- 
ence, they are gathered chiefly about the masses and 



186 ORIGIK OF THE SOLAR SYSTEM. 

particles. In a more advanced stage the collisions have 
become sharper, and the products and effects of collisions 
more conspicuous. Permanent luminosity begins to be 
maintained in the interior of the cloud, and gaseous media 
become more abundant. But I do not conceive the 
necessity of assuming that all the intervening spaces are 
filled with an}^ form of matter; since the attractions of the 
solid or liquid parts might limit the action of an expan- 
sive tendency, as has been generally conceived in refer- 
ence to the atmospheres of the planets. Meantime the 
heavier parts gradually settle nearer the centre of the 
nebulous cloud. Other nebulous clouds are precipitated 
upon this. Higher temperature, more general luminosity 
and more active rotation result. While the progress of 
aggregation continues, the evolution of a planetary system 
begins. Even at this stage we are not bound to assume 
that absolute continuity of substance extends through the 
nebula. (But see Part I, ch. i, § 7.) 

3. It is not physically probable that a ring icoidd 
ever be detached.* — As acceleration should increase the 
equatorial protuberance, the transfer of particles from 
higher latitudes, and possessing slower motion, would act 
as a brake, arresting the excessive velocity, and thus for- 
ever preventing an excess of centrifugal momentum. 

(1.) Reason and observation affirm the probability of 
a ring. — Laplace, who looked as profoundly as any one into 
the physical principles involved, was of a different opin- 
ion. And so have been nearly all writers on the subject. 
If contraction of total volume takes place, the sum of the 
radii vectores of the particles must be diminished, and 
then, if the principle of conservation of areas is not falla- 
cious, the velocity of rotation must be increased. (See p. 
106.) The increase must sooner or later exceed the limit 

*Rev. S. Parsons, Methodist Quarterly Revietc, January, 1877; Rev. W. B. 
Slaughter: The Modern Genesis, ch. iv— a mechanically abeurd objection. 



OBJECTIONS FROM COMETS, STARS AKD NEBULAE. 187 

of equilibrium between centripetal and centrifugal tenden- 
cies, to whatever extent progress toward that limit may 
be retarded by the transfer of particles from higher lati- 
tudes toward the equator. The denial of the conclusion is 
met by the rings of Saturn and the annular nebulae, by 
the rings of Plateau, and even by the projection of water 
from a rapidly revolving grindstone. 

(2.) M. Faye's objecMon considered. — M. Faye has also 
raised the objection that under such conception of the con- 
stitution of the primordial mass as was entertained by La- 
place, annulation would never occur.* The idea of Laplace 
was, as M. Faye states it f "that the sun is, except as to 
incandescence, a globe similar to our own, solid or liquid, 
surrounded by an atmosphere. This atmosphere, enriched 
without doubt by certain materials more volatile than the 
others, was formerly expanded through the influence of 
original heat, as far as the orbit of the remotest planet, the 
velocity of rotation of the central globe being propagated 
through the successive layers by means of their mutual 
friction, in such a manner as to bring into perfect agree- 
ment the rotation of the atmosphere and that of the cen- 
tral globe. Through the influence of cooling the central 
globe contracted by degrees; its velocity of rotation, and 
consequently that of the atmosphere, underwent progres- 
sive acceleration. But there is a limit which the accelera- 
tion of the atmosphere could not surpass; it is that where 
the equatorial centrifugal force was equal to gravity; all 
outside of this ceases to belong to the atmosphere, and 
ought to begin a planetary revolution about the sun. But 
here, one thing, it seems to me, is forgotten. If the cen- 
tral globe contracts by degrees, through cooling, so should 
the atmosphere. But nothing proves that it will not con- 
tract so much as not to attain the limit just stated. It 

* M. Faye, Comptes Rendus, torn, xc, p. 571. 
+ Compare Part IV, ch. iv, of the present v/ork. 



188 ORIGIN" OP THE SOLAR SYSTEM. 

would suffice that to an augmentation of one thousandth 
in the velocity of rotation of the central globe should cor- 
respond a contraction of one and a half thousandths in the 
radius of the atmosphere, to cause that the latter should 
never part with any portion, and thus should never give 
place to the formation of a planet.* 

''Modern studies have caused us to reject this concep- 
tion. For us, the mass of the sun is in a state of fluidity 
more or less complete in all its extent. There exists no 
solid or liquid surface which marks the commencement of 
an atmosphere. That which we call the photosphere is 
only the region where the progressive lowering of the in- 
ternal temperature permits certain vapors temporarily to 
condense and form a shifting zone of incandescent clouds. 
If, then, in former times, the sun possessed a greater vol- 
ume, its entire mass must have been expanded, and the 
entire mass must have undergone contraction through the 
influence of refrigeration." 

* If r and r' represent the equatorial radius of the "atmosphere" at two 
consecutive epochs, and have such values that r' = r ; and if and 0' repre- 
sent the angular velocities of the "central body" (and by hypothesis, also of 
the atmosphere) at the same two epochs, and have such values that 0' = 6 -| — ; 
then the value of the centrifugal tendency on the equator of the atmosphere at 
the two epochs will be r 6"^ and 7' 6'"^, and the condition of no augmentation of 
this tendency is expressed by equating these two values. Substituting the 
equivalents of r' and 6', the equation becomes 



re"^-- 



(-h)(-^) 



whence m = ± \' Ji {n - \) -^ n - \. 

If rn, the denominator of the fractional increase of the angular velocity, be taken 
at 1,000, then n = 500 very nearly. That is, if the angular velocity of the central 
body is increased t^iftti a corresponding decrease of tth^ 'Ji the radius of the 
atmosphere would preserve the centrifugal tendency unchanged, and no part of 
the atmosphere would be abandoned. This result, it will be noticed, assumes 
that all Ihe motion of the atmosphere is imparted by the rotation of the central 
body, and that the contraction of the atmosphere (which under the conception 
stated would be much more than that of the central liquid or solid central body) 
contributes nothing to the increase of its velocity. While M. Faye's reasoning 
is correct, it is extremely doubtful whether his premises express correctly the 
conception of Laplace. 



objectio:n^s from comets, stars and nebul.e. 189 

So far M. Faye's objection rests only against an alleged 
particular conception of Laplace. It is true that Laplace 
employs language which might justify such an interpreta- 
tion of his ideas as is set forth by M. Faye. That, how- 
ever, is of little consequence, since those who hold to a 
nebular evolution of planets are not limited to methods of 
detail which seemed satisfactory to astronomers of the 
last century. Annulation under the Laplacean conception 
may be impossible, and yet both possible and probable 
under the modern conception of the solar constitution, 
and of the primordial nebular condition of the matter of 
our system. 

But M. Faye next proceeds to show by mathematical 
reasoning that a sun constituted according to the modern 
conception would never annulate by the simple process of 
equilibrated equatorial zones.* I am persuaded, however, 
that errors have crept into his investigation, which vitiate 
his conclusion. However presumptuous it may appear to 
criticise the work of a mathematician of such masterly 
skill, it is certainly the privilege of every one to compare 
his conclusions with facts, and to scrutinize the tenability 
of his assumptions. The facts of the actual world con- 
vince us of the possibility of annulation through augmen- 
tation of centrifugal tendency. The orbital velocities of 
the planets are still such that centrifugal and centripetal 

* The general formula which he employs to express the density of the nebu- 
lar mass at any point whatever is 



d[i-(i-.)V^] 



where D represents the central density, R the radius of the solar [nebular] equa- 
tor, r the distance from any point whatever to the centre, n an arbitrary positive 
number, and a a very small fraction. This gives a very feeble final density [that 
is, when r becomes equal to R], and at the same time a decrease of density as 
rapid as may be desired, from the centre to the surface, since n may vary from 
zero to infinity, and a may be replaced by zero,— a supposition which makes the 
surface density zero. This law, M. Faye remarks, is analogous to that which M. 
Roche {Essai sur Vorigine dii systeme solaire, 1873) has employed with full suc- 
cess for the terrestrial globe, and to that of Legendre and Laplace. 



190 OEIGIIs^ OF THE SOLAE SYSTEM. 

tendencies are equalized; and simple calculation shows 
that a heated nebulous mass, under certain conditions of 
internal density, beginning contraction with an initial 
rotation however slow, will acquire increase of rotational 
velocity up to the point of annulation.* Moreover, M. 
Faye, in approaching his conclusion, assumes as one con- 
dition, that "we do not admit the planets formed at the 
expense of the sun," an assumption which conflicts not 
only with our own nebular theory, but also with that 
subsequently expounded by M. Faye himself, f He thus 
finds the moment of inertia constant in all the history of 
the sun's contraction. Again, in determining the numeri- 
cal ratio of the centrifugal tendency to the central attrac- 
tion, he obtains the value of certain quantities from the 
present condition of the sun. Among these is the rota- 
tional velocity of the sun. This, I have elsewhere main- 
tained, is an erroneous assumption, since we discover valid 
reasons for concluding that the actual solar rotation is not 
fully and simply the result of that secular acceleration to 
which we ascribe the action of ring-making. 

I conclude, therefore, that we have good physical 
grounds for maintaining that in a highly heated, nebulous 
rotating spheroid, increase of angular velocity would pro- 
ceed to such a limit that annulation would begin. 

* Let and 6' represent the angular velocities of the nebula at commence- 
ment of contraction and at an epoch when annulation is possible, and r and r' 
represent the equatorial radii of the nebula at the same epochs. To find what 
amount of contraction is necessary to increase the primitive angular velocity B 
to 6'. we have 

e-.B'v. r'2 : 7-2, 

whence 7'' = ±r\ — • 

If 0=1 and e'=A, r'^Vi r. Generallv, if e'=:Tn 6. then r'=r , — . That is, the 

\ ?n 
annulating radius varies, in diflEerent cases, inversely as the square root of the 
ratio of the primitive and annulating angular velocities, and is equal to the 
primitive radius multiplied by the reciprocal of the square root of that ratio. 
Now it is manifestly allowable to suppose such a law of variation of internal 
density that while increases to 0', r may decrease to r\ 

t See § 8 of the present chapter. 



OBJECTIOIirS FROM COMETS, STARS AN"D NEBULA. 191 

The whole discussion may be supplemented by the sug- 
gestion that the initial rotary velocity of the nebula may 
be rapid. It arises, according to the views here set forth, 
from some primitive nebular collisions. Whatever rotary 
momentum may be thus imparted will be conserved during 
subsequent contraction; and increase of rotary velocity 
will proceed from this beginning. We are at liberty to 
assume any such initial velocity of rotation as would 
necessitate annulation at any subsequent stage. 

4. The leant of uniformity in the comjyosition of the 
fixed stars. — Mr. Rutherford, in concluding a statement 
of results of the spectral examination of stars, says:* 
" We have long known that ' one star differeth from an- 
other star in glory'; we have now the strongest evidence 
that they also differ in constituent materials — some of 
them, perhaps, having no elements to be found in some 
other. What, then, becomes of that homogeneity of 
original diffuse matter which is almost a logical necessity 
of the nebular hypothesis?" To this it may be replied: 

(1.) No such universal and absolute homogeneity is 
assumed. It is not admitted that even our solar nebula 
was completely homogeneous. If we discover identical 
substances in other orbs, that is a fact pointing toward an 
ancient material connection or common origin; but if we 
find evidence of some unknown substances, that is not 
sufficient to negate the significance of so many facts 
pointing to a common cosmical history; it is rather what 
ought to be expected where the different parts of the 
material system are separated by intervals so immense. 

(2.) The indications from spectroscopic observations 
are yet too incomplete and too ambiguous to base any 
important negations on; but so far as stellar spectra have 
anything to testify, they tend wonderfully to establish the 
unity of substance throughout the visible um'verse. 

* Rutherford, Anier. Jour. Sci.^ II, xxxv, 77, 



192 ORIGIJ^ OF THE SOLAR SYSTEM. 

5. The spectra of the nehulce do not indicate sufficient 
pressure.^ — It is in this assumed that the nebular theory 
implies that the various nebulae should be in all stages of 
condensation; and hence, as different degrees of conden- 
sation give bright spectral lines of different breadths, 
some of the nebular spectra should afford broad lines. 
But as Mr. Plummer says: "From the observations of 
Huggins it would appear that the bright lines in the nebu- 
lar spectra present no appreciable thickness in all those 
cases in which it has been possible to use a narrow slit. 
The lines have invariably been found to be exceedingly jfine. 
Hence," continues Mr. Plummer, "we are furnished with 
distinct proof that the gases so examined are not only of 
nearly equal density, but that they exist in a very low 
state of tension. This fact is fatal to the nebular 
theory. '^'^ This is a most surprising example of inductive 
generalization. Only a few suggestions are required. 

(1.) The nebular theory primarily and chiefly concerns 
the origin of the bodies of the solar system from a sup- 
posed primitive nebula. The phenomena of firmamental 
nebulae have been summoned to illustrate and confirm the 
theory; but if it should be proved that such confirmation 
is wholly unattainable, the theory would still rest on all 
the analogies and physical relations which Laplace and 
many others have accepted as adequate ground of convic- 
tion. 

(2.) It seems impossible that any unbiased judgment 
should hesitate to detect in the aspects of the nebuL'e the 
evidence of the reality of their close relation to such a form 
and condition of matter as the nebular theory of planetary 
origin postulates. But the bright lines which they yield 
are not broad enough! Well, for all that, the bright lines 
declare that the nebuLne are gaseous, or at least contain 

* Plummer, Natural Science Review, IQlb-. Rev. S. Parsons, Meth. Quar.Rev., 
Jan. 1877, pp. 138-9. 



OBJECTIONS FROM COMETS, STARS AKD NEBULiE. 193 

gases, and that they are self -luminous, and their narrow- 
ness proclaims a high state of rarefaction. Here are 
three sentences of favoring testimony to oppose to one of 
unfavorable testimony. Let us see what that fourth sen- 
tence is worth. A nebula would not be a nebula unless it 
were tenuous and, in free space, so little condensed as to 
yield narrow lines. Has Mr. Plummer tried the effect of 
compressing a bit of nebula in a confined space, to see if 
its spectral lines would not widen? Next, the interior of 
the nebula is the region where tension must exist; but 
the light upon which Huggins experimented came neces- 
sarily from the exterior, where, by the laws of gaseous 
bodies, the tension must always be at a minimum. 

(3.) If nothing more were to be said, the certainty of 
the inferences drawn from width of spectral lines is not 
yet sufficiently well established to outweigh the general 
evidences that the nebulge are of such nature as has been 
commonly ascribed to them; still less to render nugatory 
the hundreds of indications manifested in the solar system 
that our planets and satellites have had a nebular origin. 
Neither, finally, can the assumed identification of elemen- 
tary substances in the nebulae be regarded as sufficiently 
certain to base on them any destructive criticism of the 
nebular theory. The correspondences of the spectral lines 
are not exact, and the inferences are merely provisional. 
The nebulae may in fact exist in a state of elemental dis- 
sociation; and even our recognized elements may occur in 
the nebulae in that state of ultimate decomposition into 
simple and universal world-stuff toward which our atten- 
tion has been directed by so many modern investigators 
(see p. 48). In such case, the spectral lines would be pro- 
duced under circumstances such as have not been created 
in our laboratories, and it would be impossible for us at 
present to give them a correct interpretation. 

So far then, as nebular spectra testify at all, they indi- 
13 



194 ORIGIX OF THE SOLAR SYSTEM. 

cate a wonderful range of common conditions between the 
nebulae and the sun, and tend, like stellar spectra, to estab- 
lish the unity of substance throughout the visible universe, 
as also unity of fundamental conditions and unity of 
dynamical activities. 

I think I have thus gathered together most of the ob- 
jections offered in recent times,* to the theory of the 
nebular origin of the solar system. Very few of these 
have been offered by scientists who have looked intelli- 
gently into the physical relations of the assumed nebulous 
matter during the progressive cooling. The objections 
offered by this class relate onty to matters of detail. The 
most numerous objections have been urged by those least 
competent to criticise, and by such have been paraded with 
greatest ostentation, and most defiant dogmatism. Many 
of the objections admitted in the foregoing list are so 
truly frivolous that I have noticed them only to forestall 
the pretence that *' numerous difficulties remain unre- 
moved." 

* An anonymous writer {North American Eeview, xcix, 1-33, July, 1864) has 
thrown aside the nebular theory as being only " a happy guess," and though con- 
forming to observed phenomena as alleged, deriving more support from its char- 
acter as a developmental hj'pothesis in harmony with the hypothesis of organic 
development, than from any sufficient ground for "the fundamental assumption 
of a nebulous matter." This writer recedes to the Aristotelian conception of 
"an infinite and endless variety of manifestations of causes and laws, witliout a 
discoverable tendency on the whole." It is quite astonishing that the recognition 
of order and unity in the method of the universe should be met, in some minds, by 
such a feeling of repugnance, while order, method and unity are the normal and 
necessary expressions of intelligence — of that Supreme Intelligence in whose 
defence they unconsciously stultify themselves. A finite intelligence does not 
exercise its high and characteristic attributes by a helter-skelter and. immethodi- 
cal production of results ; but deems it first of all essential to fix upon a plan 
under which its whole range of action shall be adjusted and unified. 

The account of the "nebular hypothesis " by Professor R. A. Proctor, in the 
last edition of the Americnn Cyclopcedia, unites the fundamental conception of 
Laplace with some of the fanciful suggestions of Spencer, and is completed with 
some of the characteri^^tic features of the meteoric theory maintained by the 
anonymous writer last referred to. For an intelligent account of the nebular 
theory, see an article by Prof. John Le Coute in Pop. Sci. Monthly, April, 1873, 
650-60. 



OBJECTIONS FROM COMETS, STARS AND NEBUL.E. 195 

The reader will notice that in many cases, several differ- 
ent admissible suggestions are offered to meet a single 
alleged difficulty.* This results from the fruitfulness of 
the physical conditions attending the nebular evolution. 
Many different modes of action for the production of a 
particular result are possible, and their conditional predica- 
tion is, therefore, perfectly legitimate. It is not to be 
alleged that we are at a loss to assign physical explanations 
for the phenomena which we witness; or that our expedi- 
ents are conflicting. Our inability to indicate specifically 
and categorically which of several possible modes of action 
has produced a given result, arises from the impossibility 
of knowing the value of certain factors in the problem, 
which would be conditioned by concomitant circumstances 
belonging to the history of the remote past. Especially 
must we always remain in ignorance of the amount, direc- 
tion and epochs of perturbative influences exerted by 
masses of matter not involved in the transformations of 
our solar nebula. It is perfectly legitimate to assume that 
these have acted in such way as to produce the phenomena 
attributable to perturbations. 

If, then, one or more rational explanations is offered 
for every assignable condition or phenomenon in our sys- 
tem, it is only an undiscerning judgment which can con- 
tinue to allege a conflict between facts and the nebular 
theory; and in view of the large array of coincidences 
with the facts which no competing theory has ever 
attempted to explain, it would seem to argue a callous- 
ness to evidence to persist in denunciation of the funda- 
mental conception as a physical explanation of the origin 
and history of our system. 

* still further explanations of difficulties are afforded by the theory of cos- 
mic tides, and these will be indicated in connection with the exposition of tidal 
actions and reactions (Part II, ch. ii, § 6). 



196 ORIGIK" OF THE SOLAR SYSTEM. 

§ 7. WHAT THE NEBULAR THEORY DOES NOT IMPLY. 

It is probably within the truth to say that much oppo- 
sition to the theory has been aroused by a mistaken inter- 
pretation of its consequences. I desire, therefore, to state 
concisely what the truth of the nebular theory does not 
imply. 

1. It is not a theory of the evolution of the Universe. 

— It is primarily a genetic explanation of the phenomena 
of the solar system; and accessorily a coordination in a 
common conception, of the principal phenomena in the 
stellar and nebular firmament, as far as human vision has 
been able to penetrate. 

2. It does not regard the Comets as involved in that 
particular evolution lohich has produced the Solar System; 

— but it recognizes the comets as forms of cosmic exist- 
ence coordinated with earlier stages of nebular evolution. 

3. It does not deny an antecedent history of the lumi- 
nous fire-mist. — It makes no claim to having reached an 
absolute beginning. The fire-mist may have previously 
existed in a cold, non-luminous and invisible condition. 
It may have emerged from the substance of the ethereal 
medium, or may have no consubstantial relation with it. 
The fire-mist and other nebulse may consist of matter in a 
state of molecular division, or in aggregates of any mass. 
Other nebula i^^^y be intensely heated and in a state of 
chemical dissociation, or their luminous phenomena may 
arise from a condition of things unknown to terrestrial 
science. We only affirm that the primitive nebula from 
which our system was evolved possessed at a certain stage 
the physical properties of an intensely heated and highly 
tenuous vapor. 

4. It does not prof ess to discover the origin of things, 
hilt only a stadium in material history. — Its starting 
point postulates matter and energy. It makes no affirma- 



WHAT THE NEBULAR THEORY DOES NOT IMPLY. 197 

tion concerning the origin of these. It leaves the philoso- 
pher and the theologian as free as they ever were to seek 
the origin of the modes of being.* It glimpses matter in 
a certain phase of existence, having active forces within, 
impelling it along an intelligible and methodical career of 
development. It stands on the regularity of nature and 
writes a history revealed to the understanding. Matter 
and force are recognized as existing realities; but in refer- 
ence to their subjective nature the theory is as silent as 
upon their origin. 

5. It does not deny the existence o/plan and purpose 
in the system of cosmic evolution. — It insists that the 
plan is so fixed that the most confident calculations as to 
the future and past may be based upon it. It holds that 
the concomitant existences and the successive stages in 
the w^hole history are intelligibly adjusted to each other; 
and as it is a system of phenomena and events which 
human thought can grasp and contemplate, it is itself, 
philosophically considered, the expression of thought, and 
implies a Thinker possessing attributes as vast as the cre- 
ation. Moreover, there is nothing in the scientific postu- 
lates or implications of the theory to contravene the affir- 
mation that as the product of intelligence it must of 
necessity involve ^9?^r/905e; and as the force which existed 
in the beginning and is the moving principle through all 
the history cannot be conceived as active without a sub- 
ject, nor as residing in an undiscerning, unthinking, invol- 
untary subject, so the whole history of cosmical evolution 
is a display as wide as the universe and as enduring as 
time, of the ever-present activity of an Intelligent Person- 
ality controlling and effectuating all the operations of 
nature. 

* " The problem of existence is not resolved. * * * The nebular hypothe- 
sis throws no light upon the origin of diffused matter. * * * The nebular 
hypothesis implies a First Cause * * * " — (H. Spencer, Yt/estminster Re- 
View, Ixx, 127, July, 1858.) 



198 ORIGIN" OF THE SOLAR SYSTEM. 

In the light of these statements, I desire to reproduce 
the opening paragraph of a review penned by a theologian 
whose profession, and whose creditable acquaintance with 
science should equally have restrained him from commit- 
ting himself to a sentiment so divergent from the facts 
and so disparaging to the interests of religion. I leave the 
paragraph as food for reflection. It is as follows: 

"Since the speculations of the evolutionists have been 
advanced with such boldness and plausibility, the nebular 
hypothesis has assumed an importance which it did not 
possess in the time of Herschel and Laplace. It is, in 
fact, the first link in the development theory by which it is 
attempted to bind together all nature in a rigid system of 
materialism, forever excluding the interposition of mind 
and the idea of a divine cosmos. Final cause is pronounced 
a chimera, and the first great cause is remanded to the 
sphere of the unknown."* 

§ 8. PROPOSED MODIFIED FORMS OF XEBULAR THEORY. 

1. 31. Faye's proposeil.. inodification. — It is indispens- 
able, in a general discussion of nebular cosmogony, to 
make adequate mention of some important modifications 
in the theory of world-genesis which have lately been 
offered by the distinguished Director of the Observatory 
at Paris. As these are applied by the author especially 
to the cosmogonic history of our system, rather than to 
nebular evolutions at large, the present is perhaps the 
most appropriate place for reproducing his views. I shall 
translate the greater part of his article in the " Comptes 
Rendus," on the Origin of tlie Solar System.^ 

"The hypothesis of Laplace is based on the preexist- 
ence of a globe possessing all the mass of the solar system, 

* Rev. S. Parsons, M.A., The Nebular HypothesU and Modern Genesis, 
Methodist Quarterly Review, IV, xxix. 127. Jan. 1S77. 
t Comptes Rendus, xc, 637, March 22, 1880. 



PROPOSED MODIFIED FORMS OF KEBULAR THEORY. 199 

and all its meclianical energy under the form of rotation. 
Through the action of an intense heat whose origin is not 
explained, the atmosphere of this globe, for to him it was 
only an atmosphere, became expanded to the limits of the 
remotest planetary orbit of our system. In cooling, it 
abandoned from time to time, in the plane of the primitive 
equator, the materials of the planets. Under this new 
form, the primitive energy subsists unimpaired, but now 
wholly in the circulations which we find existing. Thus 
by the intervention of heat and the play of centrifugal 
force, Laplace caused to be produced a totally different 
distribution of the mass and of its movements. This corres- 
ponds, to a certain point, with what we see. But this 
intervention of heat is itself a pure hypothesis. To 
justify it, we must suppose with Poisson that there are in 
the universe, regions with very different temperatures, 
and that the primitive globe, by virtue of its motion of 
translation, had passed into one of the hottest. (1) * 

"Observation leads us, meanwhile, toward other ideas. 
The nebulae, where matter is disseminated over vast spaces, 
have always produced in us and other astronomers the 
conviction that they are the point of departure of evolu- 
tions very various, and resulting in ultimate formations 
the most diverse, such as simple suns, double, triple and 
quadruple suns, and globular masses of minute suns 
reckoned by thousands. It is necessary to contemplate 
the scene, on a fine evening, with the aid of a good teles- 
cope, under the guidance of an experienced astronomer 
who has had the goodness to select beforehand appropriate 
objects. The spectator finds himself then in the presence 
of a series of forms so varied — at first rudimentary, then 
more and more evolved — in the position of a naturalist 
passing through a forest, embracing in a glance of the 

* Numerals in parenthesis refer to observations at the end of this Section. 
The foot-notes are bj- the present writer. 



200 ORIGIN OF THE SOLAR SYSTEM. 

eye, the phases in the life of the same existence, although 
these phases demand in reality, for each tree, a long series 
of years Is it not natural to be inspired by these facts, 
so much the more as our own system appertains to the 
type the most common, and the easiest to comprehend, 
that of a nebulosity at first vague, then presenting a 
central condensation, being absorbed little by little, 
regularly, into a nebulous star, and finally into a single 
sun in the dark depth of the sky? Thus heat would no 
longer appear as an exterior agent which must be invoked 
arbitrarily. We see it develop itself by degrees at certain 
points of the nebulosity as a result of the energy proper 
to a vast dissemination of materials exerting a mutual 
attraction at a distance. This is then a natural phase in 
the series of phenomena. We might even conceive an 
anterior state where the disseminated matter may have 
remained a long time dark and cold. The marvellous 
indications of spectral analysis, and the mechanical theory 
of heat fully confirm this method of viewing the subject. 

"Suppose, for the purpose of fixing these ideas, that 
the matter of our system had been thus disseminated in 
the beginning, in a spherical space having a radius a 
hundred times greater than that of the orbit of Neptune. 
Viewed at the distance of the planetary nebula whose 
parallax Dr. Briinnow has ventured to measure, this very 
year, at the Irish observatory at Dun sink, ours would 
appear with a diameter of only 5'. The density of the 
matter, supposing it continuous, would be. two hundred 
and fifty thousand million [250,000,000,000] times less 
than that of a receiver with a vacuum of one thousandth.* 



*I subjoin the following calculation: 
Let d = mean density of matter of solar system, that of the earth being 
a — its volume, that of the earth being 1, 
p = its density when expanded as described, 
R= earth's radius, 
r - radius of the supposed sphere. 



PROPOSED MODIFIED FORMS OF KEBULAR THEORY. 201 

Its temperature would be in the neighborhood of absolute 
zero, at an epoch when the stars now visible could not yet 
have been formed. In spite of this inconceivable tenuity, 
the attraction of the entire mass would be felt none the 
less in all its parts. Any molecule whatever circulating 
at the surface would have a velocity only ten times less 
than that of Neptune.* In the interior, the attraction of 
the entire mass goes on decreasing toward the centre just 
in the ratio of the distance to that pointy and realizes 

Then, since the density of the matter is inversely as its volume, we have 
p : C? :: a|7rR3 : IrrrS :: a R3 : r^, 

whence p=--ad. 

To find d, we may add together the masses of the principal bodies of the 
solar system (See Annuaire du Bureau des Longitudes, 1881, p. 135), giving 324,- 
877.923, and also the volumes, giving 1,285,833.272 (this being the value of a), the 
earth being the unit of mass and volume ; then dividing total mass by total vol- 
ume, we get mean density in reference to the earth, .2526 (which is only .0004 
less than the mean density of the sun alone). As the specific gravity of the 
earth is 5.66, and that of water in reference to air is 773.28 {Annuaire, p. 514,) we 
have 

c?=.2526 X 5.66 X 773.28=1106.79. 
Also r=2, 775,000,000 X 100=2775 X lO^, and R=3959; 

whence p= ( 3959)3 x 1,285,833.272 X 1106.79 

(2775)3 X 102* 
=.000000000000004226. 

This is the density of the matter compared with common air (which is 
14.435 times the density of hydrogen). The density compared with air exhausted 
to one thousandth is .000000000004226. Unity divided by this fraction gives 236, 
600,000,000, which expresses the density of air exhausted to one thousandth, com- 
pared with the density of the matter of the solar system when expanded to a 
sphere having 100 times the diameter of Neptune's orbit. The Sprengel air-pump 
exhausts to one millionth, and yet the air remaining in the receiver has 236,- 
600,000 times the density of the matter of the solar system when expanded as 
supposed. Further, the matter beyond the sphere of Neptune, supposing the 
distribution uniform, would have been a million times the amount of matter 
within that sphere, which is 14,419,000,000 times less than M. Faye's supposition 
makes it. This shows an immensely greater tenuity of the extra-Neptunian 
matter, or, what is much more probable, a more limited extension of the matter. 
If the matter extended only as far as Neptune's orbit, its density was a million 
times greater, or .000000004226 compared with common air, or .000000061 compared 
with hydrogen. 

*li V and V' represent the velocities at Neptune and on the periphery of the 
nebula, and r and r'' the radii of revolution, then by the principle of equal areas, 

4,2 . ^n .. ,./ . y^ whence v''^=v'^ "'"^''^iuu'^loo' ^"^ ^'~io ^' 



202 ORTCxIX OF THE SOLAR SYSTEM. 

thus, temporarily, it is true, that is, so long as the homo- 
geneity of the nebula shall endure,* an abstract concep- 
tion of central forces, the consequences of which have 
been discussed in treatises on mechanics since the time 
when Newton signalized it as a law fully as capable of 
binding harmoniously the movements of a system as that 
of gravity varying in the inverse ratio of the square of 
the distance. At that time all bodies placed within that 
vast circumference would describe, under the slightest 
impulse, ellipses or circles having their centre at the 
centre of the nebula, f For all these bodies the period of 
revolution would be the same, a thousand times greater 
than that of Neptune. | A molecule falling from any point 
whatever toward the centre would reach it in a quarter of 
that time, that is to say, in 41,000 years. 

" This nebula moves. We find in the translation of the 
sun toward the constellation Hercules, the movement of 
its centre of gravity. The total movement must be more 
complex, and embrace a slow rotation or rather a sort of 
whirlpool motion of the whole mass around a certain axis, 
as in the nebulae of Lord Rosse. But it is only in the 
plane centrally perpendicular to this axis that these rota- 
tions could become regular and persistent, because there 

* The principle would not be disturbed by any rate of increase of density, 
provided it proceeded symmetrically on all sides at corresponding distances from 
the centre. 

tSee Tait and Steele's Dynamics of a Particle. 4th ed.. 114. 

t Orbital velocities are always proportional to the central force. Therefore. 
if V, r and t represent the velocity, distance and time of any'revolving body, then 
since in this case velocities are proportional to the distances and inversely as the 

times, we mav take av. nr and—, to represent the velocitv, distance and time of 
nt ^ 

.., V- 1 , . ^ r^, , '^ I' ni '^ n 

any other bodv revolving as assumed. Therefore, — = — =-r nr — = t •'• « = '> 

nv nr t ^^ n \ 

and H t=t \ so that the times of revolution of all bodies moving as supposed would 
be equal. But the times, under the law of gravit)-, are as the cubes of the square 

roots of the distances : and for the distances r and 100 r, are as 1 to lOO^^, or as 1 
to 1000. Hence the uniform time of revolution would be a thousand times the 
period of Neptune. 



PROPOSED MODIFIED FORMS OF KEBULAR THEORY. 203 

they would adjust themselves according to the same laws 
as a circulation regulated by the proper gravity of the sys- 
tem, that is to say, of all the parts. If, then, trains of 
matter somewhat circular, in a word, rings like those of 
Saturn, or those of certain nebula?, such as 51 Messier, 
become finally established in the bosom of the nebula (2), in 
the vicinity of the primordial equator, the velocity must 
have increased from the internal border of each ring to 
the external, proportionally to the distance from the cen- 
tre, as in the case of the rotation of a solid ring. 

"All the planets proceeding from the rupture of these 
rings would continue to circulate in the primitive direc- 
tion, which we will call direct. Here is the capital fact of 
which the hypothesis of Laplace takes so good account. 
Only, their rotations should all be direct, if things re- 
mained in this state. But from the commencement, I 
mean to say from the time when this nebula became com- 
pletely isolated, there has been produced a phenomenon 
which has modified these first conditions. From all the 
regions which do not participate in these regular circula- 
tions, the materials of the nebula fall toward the centre, 
describing very elongated ellipses (3), and not circles. They 
produce there a gradual progressive condensation, in such 
a way that, disregarding a multitude of partial movements, 
the density of the nebula ceases to be uniform, and finally 
arrives at a regular rate of increase from the surface to 
the centre." 

M. Faye next proceeds to determine the direction of 
the rotation in this nebulous mass at different distances 
from the centre, and deduces an expression for the veloci- 
ty which at certain distances from the centre gives direct 
motion; at greater distances, a diminished velocity in the 
same direction; at a certain greater distance, no motion, 
and at all distances still greater, a retrograde motion con- 



204 ORIGIJT OF THE SOLAR SYSTE:>r. 

tinuing to increase in velocity to the surface.* "Thus," he 
says, "the nebula during the entire period of concentration 
is divided into two regions very different: (a) The exterior, 
where the rings in giving birth to planets, will impress 
upon them a retrograde rotation, like that of Uranus or 
Neptune; (/>) The interior, where the planets will all 
have a direct motion, like Saturn, Jupiter, etc. This is 
the singular phenomenon which our system presents, and 
against which the hyjDothesis of Laplace opposes itself 
(4). It is thus bound to a simple increase of density from 
the border to the centre of the nebula. Without doubt 
things might happen otherwise. If the rings had a pre- 
ponderant mass, they would attract to themselves all the 
matter, and would finally vacate the central regions, as in 
the nebula of the Lyre. 

" The system thus formed is by no means complete. It 
occupies at first a space much greater than our actual sys- 
tem; but in subsequent times, central condensation continu- 
ally progresses, not by cooling, be it well understood, but 
by the continued action of gravity. The planetary orbits 
were at first plunged in the diffused and rare mass of the 
nebula. By degrees this mass withdrew^ from the regions 
exterior to the orbits, and proceeded to concentrate in the 
interior, toward the centre of these same orbits. The 
areas described in a g'iven time in these circulations will 
not for this reason change, but the rings or the planets 

* The expression adopted for the law of density (see also p. 128) is 

The square of the linear velocity of the circulatory movement is 

An inspection of the factor in parenthesis shows that with increase of r the 
negative term increases more rapidly than the positive term. While it remains 
smaller, the value of the whole expression is positive, and this denotes direct 
motion; when it equals the first term, the value of the whole expression is 
zero, and when it exceeds the first term, the whole expression becomes negative, 
which means that the direction of the motion is retrograde. 



PROPOSED MODIFIED FORMS OF NEBULAR THEORY. 205 

•will gradually approach the centre, and their velocity will 
be continually accelerated, conformably to the theory 
which Laplace has given in the fourth volume of the 
Mecanujue Celeste, for the inverse case where the central 
mass goes on diminishing. Here we are not concerned 
with minute effects, since it is almost the entire mass of 
the nebula, up to about -^^-q, which marches thus in space 
from orbit to orbit, to gather itself at the centre. To this 
is added another cause, which acts exactly in the same 
manner, that is to say, the resistance of the materials 
which constantly travel through space, and fall almost 
directly toward the sun, and from nearly all sides. It is 
further evident that this double and continual contraction 
of the orbits will proceed, without altering in any respect 
the direction of the rotation of the planets or the direction 
of the circulation of their satellites. 

"As to the distances of the planets from the sun, or of 
the satellites from their planets, nothing prevents that 
they should be found to-day, beyond the limits assigned 
by Laplace. There is no more question, in fact, in causing 
to intervene here the play of centrifugal force for pro- 
ducing some at the expense of others. 

"We have assumed that the sun absorbed all that 
which was not involved in the circulation of the rings in 
the vicinity of the primitive equator. This could not be 
completely the case. A portion of the superficial nebu- 
losities, especially toward the poles, actuated by very feeble 
lateral impulsions through the influence of various causes, 
and describing around the centre very elongated ellipses, 
must have been able to traverse the central regions with- 
out being arrested there. Escaped from the agglomera- 
tion where the sun at a later period is formed, they have 
nevertheless experienced its action in numerous returns, 
and must have continued to describe elongated trajectories, 
variable in form and position, whose final term will be an 



206 OKIGIX OF THE SOLAK SYSTEM. 

ellipse having its focus in the place where the primitive 
ellipse had its centre. Undoubtedl}", here is presented the 
difficulty of the rapid contraction which the circular orbits 
have undergone; but as these portions move in elongated 
ellipses, reaching or even passing the limits of the nebula, 
they must have escaped almost completely this effect, since 
one part of their orbits lay, since their origin, beyond the 
region w^hence the mass withdrew (5). The period of 
revolution must have remained \ery considerable, and 
must have been reckoned by thousands of years, as in the 
primitive times. As to the direction of the movement, it 
will be indifferently, direct or retrograde; the inclination 
of the planes of the orbits to the primitive equator will be 
any value whatever; in a word, this will be the realm of 
the comets, which appertain so visibly to the solar system, 
though the h}-pothesis of Laplace would be compelled to 
exclude them. 

"However it may be on this delicate point, our system 
became stable from the epoch when that part of the nebula 
not involved in the planets became entirely absorbed in 
the sun. The void has been made comjDlete, as about the 
simple or double stars which we see in a dark night. It 
remains to expend the energy transformed into heat; but 
that which has conserved the method of the movement 
will remain, 

"This conservation, nevertheless, is not absolute. At- 
tractions provoke in all bodies internal strains which 
develop a little heat. Cometary masses passing near the 
sun disintegrate into nebulous trains as if for return to 
their origin. These latter proceed to collide with planets 
and engender there light and heat. Thus disappears by 
degrees a portion of the store of mechanical energy but 
this is only a feeble image of the past. 

"It remains to restore to the starting point this mys- 
terious dissemination of dark matter which contains in 



PEOPOSED MODIFIED FORMS OF Is-EBULAK THEORY. 207 

potentiality so many wonders; but this must remain the 
insuperable term which we meet in all questions of origins. 
Nevertheless, the possibility cannot be denied. The re- 
pulsive force of the sun which I have attributed to the 
action of incandescent surfaces, and where other astrono- 
mers see the play of electric forces, produces before our 
eyes, in the extremely divided matter of comets, though in 
miniature, a dissemination entirely parallel. 

"I ask for this rapid exposition, the indulgence of the 
Academy, for I am sensible how far it is from the incom- 
parable precision which we admire in the hypothesis of 
Laplace. Since the latter was formulated, the two Her- 
schels with their powerful telescopes, the American as- 
tronomers with their gigantic lenses, have taught us to 
read the heavens better. Spectral analysis and thermody- 
namics have been created. In short, Laplace was unac- 
quainted with the new conditions which observation has 
continued to reveal to us down to the most recent times. 
I have thought that the moment had arrived for attempt- 
ing to bring all these facts into coordination."* 

It will be noticed that most of the fundamental assump- 
tions of this theory are in accord with the positions taken 
in this work. That the different nebulae are destined to 
different methods of evolution I have maintained in the 
first chapter. The likeness of the stellar firmament to the 
assemblage of variously aged trees in a forest is an 
analogy pointed out by Laplace. I have argued, and so 
has Mr. Croll, that the heat of incandescent nebulae may 
be the result of the transformation of mechanical energy; 
and I have pointed out reasons for presuming that incan- 
descent nebulous matter existed previously in a cold and 
dark state. M. Faye does not hesitate to recognize with 

*See also M. Fayc's ^Vo^^ suv les idees cosmogoidqnes cle Kant, apropos 
d'une reclamation de priorite de M. Schlotel, Comptes Rendus, xc, 1246, May 31, 



208 OEIGIN OF THE SOLAR SYSTEM. 

Laplace, that nebular equatorial riugs will undergo disrup- 
tion, though the rings are conceived by him to be formed 
within the nebular mass, and not at its periphery. The 
descent of the parts of the nebula toward the centre by 
virtue of their own gravitation, is a doctrine generally 
admitted, though M. Faye assumes that other neighboring 
parts are not thus moved. That the whole nebula might 
be transformed into a ring is a conclusion which I have 
enunciated, and on different grounds. M. Faye recognizes 
the influence of meteoroidal matter in condensation, and 
the production of heat and light by collision with the 
planets; and is the first after the present writer, so far as 
known, to suggest that attractions "provoke internal 
strains which develop a little heat;" though his statement 
is a single sentence, and does not reveal any high estimate 
of the theoretical importance of the principle. 

At the same time, however, M. Faye's noteworthy 
modification of nebular cosmogony embodies some state- 
ments and princij^les on which I would like to offer a few 
s'^ecial observations: 

(1.) The circumstance that Laplace offered no explana- 
tion of the heat postulated in the primitive nebula ought 
not to weigh against the plausibility of his theory. As M. 
Faye observes, we always arrive sooner or later at questions 
of origins which, for the time being, must remain unan- 
swered. M. Faye himself has assumed more unexplained 
conditions than Laplace. If the latter finds evidence of 
the primitive existence of intense heat, its inexplicability 
is no greater evidence against its reality than the mystery 
of the aurora horealis against the reality of that pheno- 
menon. Nor was Laplace consigned to the alternative of 
accepting Poisson's hypothesis. He may have rejected it 
as improbable, and have trusted to the future to disclose a 
physical cause of the heat. Poisson's hypothesis was not 
reached by an unbroken process of scientific deduction; it 



PROPOSED 3I0DIFIED FORMS OF XEBULAR THEORY. 209 

was a hypothesis created outright })y the power of inven- 
tion. The incandescent nebula of Laplace was a state dis- 
closed to intelligence by a rational regressive process of 
argumentation. 

(2.) As to the establishment of rings '' in the bosom of 
the nebula," it w^ill be noticed that M. Faye does not assert 
the probability of its occurrence, or mention any physical 
ground on which it could be predicated, but simply says, 
"if they should become finally established," the angular 
velocity would be the same on both borders. Now a spiral 
motion, as I have conceived, implies a retarding influence 
exerted upon the exterior portions of a fluid in a state of 
rotation. While a fluid mass possessing a spiral motion 
must tend toward a symmetrically spheroidal form, the 
production of our annulus can only be a peripheral inci- 
dent; and it is certain that we know of no physical cause 
for its existence except that assigned by the theory of 
Laplace. A " whirlpool " motion may be considered to 
differ in direction from the spiral motion here contemplatec^. 
The paths described have the same form, but the parts 
converge by a winding progress toward the centre. They 
are conceived as descending by a retarded motion at the 
same time that some impulsion has deflected them from 
direct lines to the centre. Admitting that "trains" of 
particles might be able to extricate and isolate tkemselves 
sufficiently from the opposing friction of contiguous regions 
of particles, so as to flow like streams in the ocean, with a 
differentiated and special motion; admitting also, that the 
nebula as a whole possesses some rotary motion, and that 
the rate of this increases as the parts descend nearer the 
centre, what can we infer on physical grounds, as to the 
formation of rings? We cannot look for them as a result 
of motion toward the centre; thi-s tends continually to pre- 
vent rings. We cannot expect them to result from local 
tangential impulsions producing currents which flow around 
14 



210 ORIGIX OF THE SOLAR SYSTEM. 

the mass; for by hypothesis, circumferential motion is all 
the time combined with motion of descent; and besides, 
the differential motion of such currents would be destroyed 
by friction, and the currents would cease to exist; and 
finally, if they should persist, the planes of the paths de- 
scribed would sustain no common relation to a fixed plane. 
Rotation of the mass would exert no influence upon the 
trains of particles except through the development of cen- 
trifugal tendencies. These would be greatest at remoter 
distances from the axis of rotation, that is, in the regions 
where the linear motion under the law of attraction within 
a sphere would be greatest. In other words, the greatest 
velocity of descent would be opposed by the greatest con- 
trary tendency; the motion in the descending spiral would 
be somewhat equalized, and the form of the spiral would 
more nearly approach a circle. Now^ it is conceivable that 
the relative amount of the centrifugal tendency might 
become so great that the motion of descent would be 
p'ractically zero, and a train at the equator would pass into 
the form of a ring. But such ring results, it will be 
noticed, from a suspension of the motion of descent, which 
is a cardinal conception in M. Faye's theory at this point, 
and also in relation to cometic genesis; and assumes the 
controlling influence of the centrifugal tendency. In both 
these requirements the conditions of annulation become 
exactly those assumed in the Laplacean theory. It is not 
affirmed that M. Faye reasons or would reason in this way 
in followino' out the o^enesis of a rino-.^ He does not 
explain by what physical action a ring would arise; and 
all that is here stated is that if a ring could come into ex- 
istence in a "whirlpool" nebula, it would be only through 
centrifugal action, and must be peripheral and equatorial, 
as Kant and Laplace assumed. Thus, when M. Faye's 
theory is pushed through the details of ring-genesis, its 



PROPOSED MODIFIED FORMS OF J^EBULAR THEORY. 211 

peculiarities avail nothing, and it invokes the Laplacean 
principle to carry on the cosmogonic work. 

(3.) It is not apparent that portions of matter falling 
from the regions of the poles of the nebula through a 
medium in which attraction varies as the distance from 
the centre, would necessarily describe " elongated ellipses." 
Though this is a correct physical principle, and might be 
realized in a hollow sphere, it would not be within a 
nebulous sphere. The descending matter would, from the 
assumed homogeneity of the nebula, possess a physical 
state somewhat similar to that of the matter passed 
through. Its motion would therefore be retarded by fric- 
tion, and approximated to the motion of the medium by 
which it might be surrounded. But supposing those 
elliptic motions accomplished, any condensation of the 
nebula arising from the motion of these portions of matter 
toward the centre would be neutralized by the succeeding 
motion of the same portions of matter away from the 
centre. This is not to deny that condensation would take 
place, but only that the existence of " elongated elliptic 
orbits" would contribute to condensation. The " regular 
rate of increase " of density toward the centre would 
result from the consentaneous movement of parts from the 
more peripheral regions along lines more or less disturbed, 
toward the centre of gravity of the mass. 

(4.) On M. Faye's reasoning to establish the necessity 
of retrograde motions in the parts of the system remotest 
from the centre, I have had occasion to offer some observa- 
tions in another place.* I have also attempted to show 
that by properly supplementing the Laplacean conception, 
retrograde motions are provided for as well as direct mo- 
tions. 

(5.) M. Faye's speculation concerning the origin of 
comets seems particularly inconclusive. He undertakes 

* Part I, Chap. II, § 4, Ji; and Part II, Chap. I, § 2, 1, (4). 



212 origi:n' of the solar system. 

in the first place, a task unnecessarily imposed, since it 
may be rationall}^ maintained that the comets are not 
native members of our system. He proceeds, in the next 
place, in a wholesale and incautious way to consider the 
cometary masses as parts of the nebula, and then speaks 
of them as "reaching or even passhi//^^ the limits of the 
nebula, and next states that '' one part of their orbits la}' 
since their origin^ beyond tJie region whence the mass 
icithdreio.'^'' The self-contradiction here is palpable, and 
becomes a physical absurdity when we reflect that M. 
Faye attributes to an origin within the original limits of 
our nebula, cometary masses which retire to enormous 
distances beyond any supposable limits reached by the 
primitive nebula, and even traverse our system with velo- 
cities greater than could be acquired by the action of 
central forces native to the system. 

While, therefore, deeply impressed by the learned 
ingenuity of M. Faye's modification of nebular cosmogony, 
I do not as yet feel prepared to give it a preference over 
that based on strict Laplacean conceptions. 

2. &piller''s Proposed Modification. — It seems desirable 
also to notice a modification of nebular theory advanced 
by Spiller of Berlin.* He dissents from the theory of the 
formation of planets through the intervention of rings. 
According to his view planets are the product of tidal 
action combined with centrifugal tendency. This action 
is exerted upon the central mass after reaching the con- 
dition of igneous fluidity. It is manifest tliat a separated 
planetary mass must produce a tidal swell of some magni- 
tude upon the fluid central mass. This tide would be 
turned always in the direction of the planet — an antitide 

* Philipp Spiller: Die Weltsdiopfang vom Standpunke dr heutigen Wissen- 
schaft. Mit neaen Untersuchungen, 1868. 2cl ed. 1873; Die Entstehung de?- Welt 
and die Einheit der Natarknifte. ropuldre Kosmogoiiie. See also the same 
writer's important work. Die Vrkrafl des Weltal'.s nachihrem Wesert und Wirken 
avf alien Nat argebieten. Fiir Gebildele jeden Standes. 374 pp. Berlin, 1879, 



PROPOSED MODIFIED FORMS OF NEBULAR THEORY. 213 

moving simultaneously on the opposite side. It is manifest 
also that the magnitude of the tide would increase with 
the proximity of the planet, and still further with the con- 
junction of two or more planets. At some perihelion of 
the planet, therefore, — concurring perhaps with a conjunc- 
tion of planets — the centrifugal tendency of the equatorial 
portion of the central fluid mass would exceed gravitation, 
and the tidal swell would be lifted bodily from connection 
with the central mass and move centrifugally to such dis- 
tance that a state of equilibrium would be reached. The 
mass thus detached would at once assume a spheroidal 
planetary form. Thus it is supposed Uranus was detached 
as a tidal swell raised by the attraction of Neptune; Sat- 
urn, by a similar action of Uranus, and so on. As to 
Neptune, it must be admitted that the separation took 
place solely through the tangential momentum at the 
equator of the original mass, or it must be presumed that 
a tidal effect was produced by the presence of some ex- 
ternal body.* 

This theory possesses the merit of explaining the ellip- 
ticity of the planetary orbits as a primary result, and of 
dispensing with rings and thus avoiding the problem of 
planetation from rings. But on the contrary it encounters 
great difficulties. It is necessary to show the probability 
of the non-formation of rings during the nebulous stage, 
or else to explain their subsequent disappearance without 
the production of planetary bodies. It is also necessary to 
show that the central mass ever possessed such velocity of 
rotation as to detach a tidal swell from a liquid spheroid — a 
difficulty increased by the comparative insignificance of such 
a swell on a body possessing the relative mass of the sun. 
But the greatest difficulty is presented by the fact that 

* The reader will note that Spiller's conception is the prototype of Mr. G. 
H. Darwin's (noticed hereafter) concerning the retirement of the lunar mass 
from the semi-fluid earth. 



214 oriCtIX of the solar system. 

the sun has not yet attained a liquid condition, according 
to the views of modern astronomers, and there is no likeli- 
hood that its temperature had subsided to any lower point 
than the present at any epoch in the past. While there- 
fore, Herr Spiller has offered a theory which is thinkable 
and consistent with the laws of nature, it does not seem 
to be one which represents the actual history of nature.* 

* The writer intended to notice the seemingly important work of M. Roche, 
entitled Si/r Vongine du Systhne Solai7'e, published by Gauthier-Villars, Paris, 
1873, but though ordered repeatedly from booksellers in Paris, Berlin and Leipzig, 
no copy of it has been obtained. 



CHAPTEE 11. 

GENERAL COSMOGONIC CONDITIONS 
ON A COOLING PLANET. 



Und ob Alles im ewigen Wechsel Kreist 

Es beharret im Wechsel eiu ruhiger Geist. — Schiller. 

Opinionum commenta delet dies, naturae judicia confirmat. 

Cicero, de Nat. Deor. 



§ 1. RELATIVE AGES OF PLANETS IN A SYSTEM. 

ACCORDING to the nebular theory here accepted, 
-^^-^ the ages of the planets must be graduated according 
to their distances from the sun. The remotest planet at 
present known is Neptune. Its existence, before discovered, 
was pointed out by certain perturbations in the next interior 
planets, which were not fully accounted for by the attrac- 
tions of any known body. There still remain some residual 
disturbances which have led to the conjecture that a still 
remoter planet exists. This opinion was shared by my 
late honored colleague, Professor James C. Watson. For 
similar reasons Mercury for many years has been doubt- 
fully regarded as the most interior planet. Dr. Lescarbault 
announced that such planet had actually fallen under his 
observation, and he designated it Vulcan. But other ob- 
servers were not able to verify the alleged discovery. 
During the total eclipse of July 29, 1878, Professor 
Watson, in charge of observations in Wyoming, devoted 
his entire attention to the search for intra-Mercurial planets, 
and succeeded in satisfying himself that one or two came 

315 



216 A COOLIIS^G PLAN"ET. 

within the range of his instrument.* Professor Lewis 
Swift also reported from Denver some similar observa- 
tions.f The great difficulty of exact determinations during 
the few seconds of totality of an eclipse, and the absence 
of other corroborative observations, have led many astron- 
omers to adhere to the opinion that Professors Watson 
and Swift mistook fixed stars for planets. 

But the stage of development of a planet does not 
depend alone on its age. Planetary evolutions rest finally 
on progressive cooling. The condition of a planet as a 
whole is determined by the temperature of the mass. 
After incrustation, the state of the surface depends less 
and less upon the temperature of the interior, since the 
rate of conduction of interior heat through the crust con- 
tinually diminishes. But a large mass, other things being 
the same, retains a high temperature longer than a smaller 
one. A small planet may become totally refrigerated, 
while a large one of greater age may linger in a state of 
self-luminosity. The length of time the heat of a planetary 
body will endure, depends, then, on mass and extent of 
radiating surface. As the ratio of the masses is greater 
than that of the surfaces, the relative length of time a par- 
ticular phase will endure is greater than is indicated by 
the relative masses of the planets. In other words, if one 
planet has twice the mass of another, their densities being 
the same, the duration of a certain phase of cooling will 
be more than twice as long as in the other. J 

* See his communications vaAmer. Jour. Sci. Ill, xvi, 280-3, 310-13, Sept. and 
Oct., 18T8. 

t L. Swift, Amer. Jour. Sci. HI, xvi, 313-15. See also, Science, 26 Feb. and 
23 Apr. 1881. 

:{: If A and A' represent the rates of radiation of two planets, r and ?•', their 
radii, H and H' the total heat in the two, and p and p' their respective densities; 
then since the rates of radiation are as the surfaces, 

A r'2 
A: A' :: r2 : r'"- \ .-. A' = — --• 

And since the total amounts of heat are as the masses, 

H : H' :: pr^ : pV3 : .-. H' = ^, » 
prs 



PASSAGE TO THE MOLTEN^ PHASE. 217 

§ 2. PASSAGE TO THE MOLTEN PHASE. 

A planetary body is to be conceived as existing, at a 
certain epoch, in a state of fire-mist. In this state a por- 
tion of the matter exists in minute liquid particles which 
are held in suspension in the gases which constitute the 
remaining portion. Some chemical compounds probably 
exist, but others, evidently, are still prevented by the 
intense heat from forming. The gases, deeply seated 
beneath the surface, are subjected to an enormous pres- 
sure which reduces them to a density approaching that of 
the liquefied material, or even exceeding it. At some 
epoch the molten matter must descend toward the centre 
until it reaches a zone where its density is equalled by the 
density of the compressed gases. If this zone of liquid 
precipitation is distant from the centre, it will gradually 
subside toward the centre, in proportion as heat escapes 
from the condensed gas, and it thus passes, under the 
enormous pressure, into the liquid state. Ultimately, 
therefore, the planet will consist of a liquid nucleus sur- 
rounded by an atmospheric fire-mist yet too intensely 
heated to permit all its constituents to pass out of the 
aeriform condition. Progressively, however, the atmos- 
pheric envelope will transfer itself by precipitation to the 
liquefied nucleus. Meantime some portion of the atmos- 
pheric constituents will retain their gaseous condition 
below any temperature which we have experienced. The 
result will be a molten globe surrounded by an aeriform 
atmosphere. 

If T represent the relative time required for a planet to pass through a cer- 
tain phase of cooling, then 

T=5. 

A 

In this expression, since H varies (the density remaining the same) as the 
cube of the radius, and A, as the square of the radius, it follows that T varies 
more rapidly than the mass of the planet. We may also deduce 

T^ = T^'.^'. 



218 A coolixCt planet. 

§ 3. SUPERFICIAL SOLIDIFICATIOX FROM COOLING. 

At a certain temperature of the molten sea, certain 
compounds will begin to solidify in crystalline forms. 
These will float in the liquid magma, in accordance with 
a principle which I venture to regard as a general law of 
matter. Many substances, in passing from a liquid to a 
solid state, slightly increase in bulk. This is notoriously 
true of water and ice, and of type-metal. It is also true 
that solid lava floats on molten lava, a notable instance of 
which we have in the crater of Kilauea, solid glass on 
molten glass, and solid iron on molten iron. It is quite 
true, however, that a piece of iron may be taken so cold 
that its density exceeds that of molten iron, in which case 
it will at first sink. But after becoming heated and ex- 
panded, and long before the fusing temperature is reached, 
the iron will rise to the surface.* It is hardly to be 
doubted, therefore, that solidification from cooling would 
begin on the surface and gradually extend downward. f 

*0n floatingiron. see Coller/e Courant, 13 Apr., 1872, p, 1T3; Xature, May 10, 
1877, 23: 8 Aug., 1878, 397, for conchisive experiments; 29 Aug. 1878, 464 and vol. 
xvi. 23. For Mallet's apparently conflicting results, see Nature, Xo. 156, ab- 
stract in Amer. Jour. Set., Ill, viii, 212, and for a reply to Mallet, see A. Schmidt, 
Amer. Jour. Sci., HI, viii, 287. Compare, also, Sir William Thomson, Trans. 
Geol. Soc, Glasgow, vi, 40, 14 Feb., 1878. Some recent experiments show that 
molten steel has a specific gravity of 8.05, while cold steel is 7.85 (Nature, xxvi, 
i:?8, June 8, 1882). On floating lava, see Scrope: Volcanoes. 84, 477: Kaemtz: 
Meteorology, 152; G. P. Marsh: Man and Natur'e, 545; Miss Bird: Ilauaiian 
Archipelago; Nature, xi, 324; Miss C. F. Gordon-Cumming: Fire- Fountains, 
the Kingdom of Hawaii etc., 2 vols., 8vo., 1883. On experiments with '-Rowley 
Rag,"' see Chemical News, xviii, 191. 

t Sir William Thomson, nevertheless, entertains the opinion that solidifying 
masses would sink to the centre; and he has enunciated, in harmony with Hop- 
kins, the somewhat fantastic theory that the sunken masses would build up a 
honey-combed structure to the surface, and '' masses falling from the roofs of 
vesicles or tunnels," might produce earthquake shocks: Secular Cooling of the 
Earth, Trans. Roy. Soc, Edinb., 1862; Thomson and Tait'e Natural Philosophi/, 
§§ (ee), iff): Glasgow Addre.^s. 1876. Amer. Jour. Sci., Ill, xii. 346-7: Trans. 
Geol. Soc, Glasgow, vi, 40-1, 14 Feb., 1878. In the latter paper, however, he 
expresses himself with less confidence. On this subject see Hopkins: Researches 
in Physical Gtology: Phil. Trans. Roy. Soc, Pt. II, 1839, quoted in his Report io 
Biitish Assoc, 1847. p. 33. 



SUPERFICIAL SOLIDIFICATION FROM COOLING. 219 

As a final illustration, I venture to quote from Mr. W. 
Matthieu Williams* a description of what takes place in 
the "open hearth finery and the refining of pig-iron." 
"Here a metallic mixture of iron, silicon, carbon, sulphur, 
etc., is simply fused and exposed to the superficial action 
of atmospheric air. What is the result? Oxidation of 
the more oxidizable constituents takes place, and these 
oxides at once arrange themselves according to their spe- 
cific gravities. The oxidized carbon forms atmospheric 
matter and rises above all as carbonic acid, then the 
oxidized silicon being lighter than iron floats above that 
and combines with aluminium or calcium that may have 
been in the pig and with some of the iron ; thus forming 
a silicious crust closely resembling the predominating 
material of the earth's crust. 

"When the oxidation in the finery is carried far enough 
the melted material is tapped out into a rectangular basin 
or mould, usually about ten feet long and about three feet 
wide, where it settles and cools. During this cooling the 
silica and silicates — i.e., the rock matter — separate from 
the metallic matter and solidify on the surface as a thin 
crust, w^hich behaves in a very interesting and instructive 
manner. At first a mere skin is formed. This gradually 
thickens, and as it thickens and cools, becomes corrugated 
into mountain chains and valleys much higher and deeper 
in proportion to the whole mass than the mountain chains 
and valleys of our planet. After this crust has thickened 
to a certain extent, volcanic action commences. Rifts, 
dykes and faults are formed by the shrinkage of the metal 
below, and streams of lava are ejected. Here and there 
these lava streams accumulate around their vent and form 
isolated conical volcanic mountains with decided craters, 
from which the eruption continues for some time. These 

♦Williams: Discussions in Current Science, cli. vii, '•Ilumboldt Library," 
No. 41, p. 25, Feb., 1883. 



220 A COOLTXG PLAXET. 

volcanoes are relatively far higher than Chimborazo." The 
materials of the lire-formed crust of a planet must simi- 
larly pass through the stages of oxidation and silication, 
and the incidents of progressive cooling must be fairly 
represented by the phenomenon above described. 

§ 4. INTERNAL SOLIDIFICATION FROM PRESSURE. 

While incrustation begins, or even long before it be- 
gins, solidification may be produced in the central regions, 
in a planetary mass sufficiently large, by the great pressure 
of the superincumbent portions. But in recognizing the 
probability of a solid central portion, it must not be sup- 
posed that the matter is less hot than if a molten liquid. 
Any portion of such solidified interior, if brought to the 
surface, would be instantly liquefied. But at some point 
between the centre and the surface, the condensation may 
not be sufficient to produce solidification, and the reduc- 
tion of temperature may not be sufficient to cause it. 
There would then be a liquid zone interposed between a 
solid crust and a solid nucleus. That zone might be so thin 
and so variable in its thickness as to suffer actual inter- 
ruption of continuity. It would then exist as separate 
lakes in regions more or less removed from each other, 
and the rigidity of the planet would be very nearly such 
as is due to complete solidification. But even if a solid 
crust were separated from a solid nucleus by a continuous 
liquid zone, it does not appear to me that under the 
actions of the planetary system, the planet would be want- 
ing in any of the astronomical properties of complete 
solidity. I do not conceive that the crust would be likely 
to slip around the core, since, whatever action should be 
exerted upon the crust would be exerted correspondingly 
on the parts beneath the crust. The several interior zones 
in a rotating oblate spheroid, would present the same rela- 



MAXIMUM INTERNAL TEMPERATURE. 221 

tive equatorial protuberance as the external zone, and 
would all be moved synchronously and proportionally. 

The liquid zone would not pass by an abrupt transition 
downward into the state of the solid core; but would pre- 
sent gradually increasing degrees of viscosity. The same 
might be true of the passage upward into the solid crust. 

Whether a liquid zone should exist or not, it is ap- 
parent that in case of the removal or diminution of the 
pressure over any portion solidified by pressure, this 
would instantly be followed by the liquefaction of such 
portion. Hence a deep fissure through the external crust 
might be followed by the passage of large volumes from 
the solid to the liquid state.* 

§ 5. MAXIMUM INTERNAL TEMPERATURE OF AN 
INCRUSTED PLANET. . 

The progress of cooling, down to the time of the first 
incrustation, w^ould be promoted by a convective circula- 
tion between the central and peripheral parts, or, in case 
of central solidification, between the solid core and the 
periphery. The effect would be to equalize the tem- 
perature of all parts of the planetary mass.f It might 
be supposed, therefore, that at the epoch of first incrusta- 
tion the whole temperature would be but little above the 
point at wdiich solidification from cooling might begin. 
Thus the maximum temperature of the heated interior of 
a planet might be coneeived to be about that at which the 
matter of the planet liquefies under the atmospheric pres- 
sure on the planet's surface. Asa larger planet implies both 
a greater mass of atmosphere and an intenser gravitating 

* These matters will be more particularly discussed in treating of the earth. 

t Sir William Thomson has shown that if the rate of increase of tempera- 
ture in penetrating the earth should be found to suffer a diminution at greater 
depths than have been as yet explored, this fact would imply a uniform internal 
temperature below a certain depth {Trans. Geo. Soc, Glasgou\ vi, 45). 



222 A COOLIXG PLAXET. 

power, both causes would increase atmospheric pressure, 
and hence lower the temperature at which incrustation 
would begin. This implies that the central portion of a 
large planet is less hot, and must consequently require a 
shorter period for cooling, aside from the consequence of a 
greater amount of heat to be radiated. Inferior density 
would operate in the same direction. For these two 
reasons, therefore, the larger planet should not linger pro- 
portionately long in the highly heated stages. 



§ 6. TIDAL ACTION AXD ITS CONSEQUENCES IN 
PLANETARY HISTORY. 



I believe that the geologist who had studied all the text-books in exist- 
ence might still be unacquainted with the very modern researches [on palseozoic 
high tides] which I am attempting to set forth. Yet it seems to me that the 
geologists must quick)}- take heed of these researches. They have the most 
startling and important bearing on the prevailing creeds in geology. One of 
the principal creeds they absolutely demolish.— Prof. R. S. Ball: Nature, 
Dec. 1, 1881. 

The ebb and flow of the tidal wave, therefore, consists not only in an 
alternate rising and falling of the waters, but also in a slow, progressive 
motion from east to west. The tidal wave produces a general western current 
in the ocean.— J. R. Mayer: Celestial Dynamics. 

1. Some Elementary Principles. — The influences of 
cosmical tides are various, important, and everywhere felt. 
Tidal movements aie as universal as gravitation itself; 
and late researches have shown that cosmic tides have 
been deeph' concerned in the establishment of the planet- 
ary relations observed in our system. x\ tide may be 
defined as the prolateness of a body resulting from the 
attraction of another body. As no matter is known to 
exist which is absolutely rigid and incompressible, there 
can be no state of solidity so absolute as to be exempt 
from the liability to tidal deformation under the gravita- 
tional power of cosmic masses. Between absolute solidity 
and perfect molecular mobility exist all grades of consist- 
ency, from ordhiary solidity through the various degrees 



TIDAL ACTION IN PLANETARY HISTORY. 223 

of viscosity, liquidity and gaseit}'. These various condi- 
tions of matter are themselves relative to pressure, tem- 
perature and gravitation; since, at a given pressure, all 
substances pass, with increase of temperature to the 
liquid and aeriform conditions; and at a given temperature, 
however high (within certain limits), all substances pass, 
with increase of pressure, to the liquid and solid condi- 
tions; and at given pressure and temperature, all sub- 
stances tend more and more, under increase of gravity, to 
behave like liquids, and under diminution of gravity, to 
behave like gases. Moreover, there is no solidity so com- 
plete that in the presence of the mighty forces of nature, 
the substance does not yield like the simplest liquid. In 
fact, it may well be doubted whether the attractions 
exerted by the sun and planets feel to a very important 
extent, a difference in the resistances offered by the solid 
and liquid states upon the bodies subject to their influ- 
ence. The most stubborn granites, diorites and quartzites 
may probably be conceived as fluids in relation to all the 
greater cosmic forces.* 

Tidal results depend upon the unequal influences 
exerted by an attracting body upon the nearer and re- 
moter parts of the body influenced. The attraction 
exerted by one body upon another produces the same total 
result as if the whole force were applied at the centre of 
gravity. But meantime, the different parts of the affected 
body will be set in motion in respect to each other, be- 
cause, being at different distances from the attracting 
body, they are acted on with different intensities of force. 
The parts nearest the attracting body will be more strongly 
influenced than the more central parts, and will conse- 
quently manifest a stronger tendency than the more cen- 

*For an impressive view of tlie magnitude of sncli forces, see an article by 
C. B. Warring, in Pop. Set. Monthly, xvii, G12-8, Sep., 1880, and a similar one by 
E. L. Larkin, in Kansas City Rev. of Sci. and Industry., vii, 96-9, June, 1883. 



224 A COOLIXG PLAXET. 

tral parts toward the attracting body. They will begin to 
retire from the more central parts, and will actually move 
away from them until restrained by the cohesion of all the 
parts with each other, and by the tendency of all masses 
of matter to retain the spherical form. The restraining 
influence of the last-named tendency is the same for all 
states of matter where the mass is the same; but the 
restraining influence of mutual cohesion of parts varies 
with the state of the matter. A given attraction will 
therefore produce a greater tidal result in an aeriform 
or liquid body than in one which is viscid or nominally 
solid. 

But further, the central parts of a body influenced by 
a tidal attraction yield more than the remotest parts. 
They tend, therefore, to leave the remotest parts behind, 
and these become drawn out into a retral prolongation 
until restrained and held down by mutual cohesions and 
the law of sphericity. We have, therefore, a tidal protu- 
berance on two opposite sides of the body, produced sim- 
ultaneously. They are a tide and an anti-tide. The two 
tidal curves are similar; they are produced by the same 
forces, but the curve of the anti-tide is reversed in respest 
to the curve of the tide. The force raising it is a deficient 
attraction; it is virtually a force acting in the opposite 
direction from the real attraction. In short, the anti-tide 
may be conceived as produced by the attraction of another 
body situated on the side opposite the real tide-producing 
body; and this may be designated the anti-tide-producer. 

The anti-tide, however, is somewhat less than the tide. 
The excess of attraction producing the tide is greater than 
the deficiency of attraction producing the anti-tide. This 
would not be the case if the attraction diminished simply 
with increase of distance. Attraction diminishes with 
increase of the square of the distance. 

There are three conceivable general cases under which 



TIDAL ACTIOIT IN PLANETARY HISTORY. 2^5 

tidal actions may be exerted.* (1.) Where the tide-bear- 
ing body is homogeneous, or varying in density toward 
the centre according to some fixed law. Here every^^ 

♦The statements made in the present connection on the subject of tides, 
embrace only such generalities as concern the main course of planetary evolu- 
tion. Any particular case, like the oceanic tides on the earth, may involve 
numerous considerations of which no account is necessary here — such as 
variations in distance of tide-producer; changes in declination in reference to 
equator of tide-bearer; interferences of tidal actions of two or more tide- 
producers; consequences of different rates of change of right ascension of 
different tide-producers; the absolute angular velocity of the tide-producer in 
its orbit; rotation and oblateness of tide-bearer; depth and variations in depth 
of enveloping film ; relative density of film, its actual index of viscosity, its 
actual density and its friction against resistances. In our general view it 
will only be necessary to regard the relative tidal efficiency of the tide-pro- 
ducer, the relative mass and volume (radius and density) of the tide-bearer, 
and the general fact of axial and orbital movements. 

Xo theory of tides has been mathematically worked out, which answers all 
the requirements of tidal phenomena in the tei-restrial waters. The funda- 
mental conceptions embodied in the "Equilibrium Theory" of Newton and 
Daniel Bernoulli are undoubtedly correct; but this theory neglects many modi- 
fying conditions in the actual case, and therefore fails in many particulars. 
But it is not just to pronounce it "contemptible,'" as Sir G. B. Airy has done. 
The "Dynamical Theory" of Laplace, generally considered more rational, 
though also severely criticised, conceives each particle of the water in motion, 
and investigates the forces acting on it. The tidal swell results from the tlowof 
water on both sides toward it, and the ebb results from the flow in both directions 
away from it. The working out of the theory, however, has to assume, con- 
trary to the facts, that the earth is completely covered with water, and that it is 
of uniform depth throughout any parallel of latitude. The " Wave Theor}%" 
expounded by Sir G. B. Airy, is based on the laws of movement of waves along 
canals relatively shallow and narrow, and applies especially to the motion of 
tidal waters in shallows, estuaries and rivers, where the other theories fail; 
but for the phenomena of the open sea, it makes the false assumption that the 
wave is restricted to narrow canals, instead of spreading freely in all direc- 
tions. For our present use, the conceptions of the Equilibrium Theory are 
entirely adequate. 

The completest general exposition of tidal theories may be found in Airy's 
article on Tides and Waves, in Eacyclopcedia Metropolitana, vol. v, pp. 241*- 
396*. For the purposes of the general student, however, a much more satis- 
factory general exposition may be found in the Appendix to Johnson's Cyclo- 
pcedia, by Gen. J. G. Barnard, See also. Prof. Wm. Ferrel's Tidal Researches, 
Appendix to U. S. Coast Survey, 1874, or thereabouts. See also, as collateral, 
Ferrel's papers on the Motions of Fluids and Solids Relative to the Earth's Sur- 
face, in eight communications to the Mathematical Monthly, Cambridge, Mass., 
1859-60, vols, i and ii; also, his 3rethods and Results of Meteorological Researches, 
for the Use of the Coast Pilot, Part I, 1877, Part II, 1880 (on Cyclones, Water- 
spouts and Tornadoes). 
15 



226 



A COOLIXG PLAXET. 




Fig. 38. — Co.MPorxD Tide. 
a m, tidal elevation iu less viscous 

envelope. 
c, tidal depression in less \is- 

cons envelope. 
e t, tidal elevation in more viscous 

nucleus. 
r g, tidal depression in more vis- 
cous nucleus. 
mt., depth oi" envelope at mean 

tide. 
a t, depth of envelope at high tide 

over nucleus supposed rigid. 
ae, depth of envelope at high tide 

over yielding nuchus^o f - f^ 
cr, depth of envelope at low tide 

over nucleus supposed rigid 
c g, depth of envelope at low tide 

over yielding nucleus = cr-\- 

rg. 



successive layer undergoes tidal 
disturbance according to its dis- 
tance from the centre. The 
whole bod}^ is, therefore, sym- 
metrically transformed, and be- 
comes a prolate spheroid, with 
a prolate axis a h, Figure 37, 
varying inversely as the coeffi- 
cient of viscosity. This we will 
designate a deformative tide. 
Here in o n p is a section of 
the undisturbed sphere, and 
a ch d 2i. section of the body 
when rendered tidally prolate. 
The tidal elevation is expressed 
b\^ a rn and the depression by 
c. (2.) Where the tide-bear- 
ing body consists of a cen- 
tral part, rts u. Figure 38, 
having a higher coefficient of 
viscosity than the surrounding- 
part. Here the nucleus will 
yield in a less ratio than the 
envelope. The prolateness of 
the envelope, but for the influ- 
ence of relative rotation, will 
be the same as if the whole 
body were of' the same sub- 
stance as the envelope, and the 
prolateness of the nucleus will 
be nearly the same as if the 
envelope were absent. The 
tidal fluctuations in the en- 
velope are expressed as in the 
deformative tide; but the re- 



TIDAL ACTION IK PLANTETARY HISTORY. 



227 



suiting depth of the envelope over the tidally raised 
nucleus, will be the depth resulting in case of a rigid 
nucleus, diminished by the amount of the actual tide in 
the viscid nucleus. (3.) Where the tide-bearing body 
consists of a perfectly rigid nucleus, r t s u^ Figure 39, 
and an envelope susceptible to tidal action. Here, also, 
the prolateness, disregarding rotation, becomes the same 

as if the whole body were of 
the matter forming the envel- 
ope. The dimensions of the 
tide in the envelope will be ex- 
pressed as before; but the total 
depth, a t, of the envelope at 
high tide, will not be diminished 
by any tide in the nucleus; nor 
will its depth, c r, at low tide, 
be increased by any ebb in the 
nucleus. Though it is doubtful 
whether this case exists in na- 
ture, we have to deal with cases 
where the nucleus is more or less rigid, and the degree of 
rigidity is indicated by the difference between a e, Figure 
38, the actually measured depth, and a t, the depth calcu- 
lated on the hypothesis of a perfectly rigid nucleus. This 
difference shows the amount of tidal yielding in the nu- 
cleus. But even this operation, however desiderated, has 
not been satisfactorily accomplished in practice. 

The total vertical fluctuation of the tide is the sum of 
the flood and ebb tides; or in Figure 38, it is am. 4- o c. 
The flood tide rises twice as high above the mean sphere 
as the ebb tide falls below it. This is apparent from the 
general consideration that the deficiency of fluid causing 
the ebb is spread over a greater surface than the excess of 
fluid causing the two flood-tides. The one is spread over 
a broad zone encircling the ellipsoid, while each flood-tide 




Fig. 39. — Film Tide. 



228 



A COOLIK"G PLAN'ET. 



is spread over a circular area of about one-fourth the 
extent. Each circular area, nevertheless, is more than a 
quadrant in breadth, having a radius, in a homogeneous 
spheroid, of 54° 44'. 

The tidal effect on the same tide-bearer, is directly as 
the mass of the tide-producer, and inversely as the cube of 
its distance. But for any other tide-bearer, the effect is 
also proportional to its radius.* 



These principles result from the following reasoning: 
C 




Fig. 40.— Quaxtitativb Relations of Tides, 

Let D = E M (Figure 40)= distance between centres of tide-bearer and tide 
producer, 

m — mass of tide-producer, 
E = E B = radius of tide -bearer. 
Then the attractions at B, E and A are expressed by 
m 
(D-R)2" 

Subtracting the second from the first, and the third from the second, we 
get, very nearly, 






K)2 



Excess of attraction at B over E ; 



Excess of attraction at E over A. 



2wR 

2 m R 

1)3 

But the latter is actually a little less than the former. 

TliL'^e expressions show that the efficiency of the tidal force of the same tide- 
producer vurits d'lrecl'y as the radius of (he tide-bearer and inversely as the cube 
of (he distance of (he tide-producer. 

Now, further, if we assume any point P, on the surface of the tide-bearer, 
at the angular distance </> from the line E M, joining the centres, and put {/for in- 
tensity of gravity on tide-bearer, and p for the relative density of a thin external 
film covering a rigid nucleus, then the elevation (or depression) of P above the 
!-nrface of the equivalent sphere, expressed in terms of radius (assumed as 
ur.itv^, will be 

Srn 1 



2B.!,-.-iip*™^'*-i' 



0) 



TIDAL ACTION IN PLAKETAKY HISTORY. 229 

There is another cause of tidal protuberances in certain 
cases. Suppose two bodies in space having equal masses 
and densities revolve about the common centre of gravity 
between them. Now, each is in a position to create tidal 
effects on the other through the operation of gravitation, 
as just explained. But, in addition to this, the differential 

This is a general expression for the height of any point of a film-tide having 
the relative density p (that of the nucleus being unity). 
If the spheroid is homogeneous, that is, if p = 1, 

'^=2-^-t(^««^*-i)- - (2) 

If, in the homogeneous spheroid we take ^ = 0° or 180°, then cos2 </> — i = |^, 
and 

T' = I .^= height of flood- tide, (3) 

If we take <^ = 90° or 270°, then cos 2 (|) - 1 = - i and 

T'' = - f . r— — = depression of ebb tide. - - - . - (4) 

It may be added here that, in the case of the earth, p = yi, and using this 
value, 

T' = ll .=—- = theoretical mean flood-tide. (5) 

while T'^ = — ^5 . — — = theoretical mean ebb-tide. - - - - (6) 

- - y a JL)3 g 

To find at what angular distance from the zenith of the tide-producer the 
tide in a homogeneous spheroid is 0, we have the equation, 

in which as <^ is the only variable quantity we must have cos2 <|) = i, or cos <|) = 
1^= .57735 = cos 54° 44'. This ai-c then, is the radius of the spherical menis- 
cus formed by the flood-tide or tidal protuberance. 

To render the formula (1) more general, we must introduce the radius of the 
tide-bearer as a factor, and this gives 

_, 3mR 1 / T^ 1, /-v, 

^^SD^-W^^^^^^'^-i-)- ^'^ 

If, in any other couple tidally connected, the quantities D, R. m, g have the 
values d,r, n, g', the height of the tide will be 

whence 1 = - • 4 • ^ • ■^- But if M and M' be the masses of the two tide- 
T m R d3 g> 

bearers in these values of T and t, then g' =^ g ^ ' — ^' ^>-i'l substituting, 

rf2 ' ri ' W' m, 
This gives the height of the tide on one spheroid with one tide-producer In 
terms of the height of the tide on another spheroid with another tide-producer. 



230 A COOLING PLANET. 

centrifugal tendency on the nearer and farther sides of 
each in respect to the common centre of gravity, will im- 
part to the farther side a tendency to recede from the 
centre, and to the centre a tendency to recede from the 
nearer side. The result must be the same as when similar 
tendencies are produced by gravity. The body becomes a 
prolate spheroid. This prolateness becomes important 
where a body of considerable volume revolves with ra- 
pidity in an orbit comparatively small, as when a body of 
small mass and low density revolves rapidly about another 
of large mass. But in a couple like the earth and moon 
where the centre of gravity lies so near the centre of the 
larger body,* this cause would hardly produce a percepti- 
ble prolateness of the larger body. In aeriform masses of 
matter, however, where the volume is generally great, and 
cohesion of parts a minimum, we might expect this cause to 
become quite preceptibly operative. A tidal deformation 
produced by this cause alone would tend to transfer the 
heavier parts of the body to the remoter side, and leave the 
lighter upon the nearer side. But this action could only 
coexist with proper tidal action, which alone w^ould create 
a tendency in the heavier parts to pass to the nearer side, 
leaving the lighter to occupy the remoter side. The cir- 
cumstances under which one of these tendencies would 
prevail over the other in a body (like our moon) turning 
always the same side toward the tide-raising body (like 
the earth) have been heretofore discussed. [Part I, Chap, 
ii, § 4, 3, (2).] If the rotary and orbital motions are not 
synchronous, the effect of tidal action upon the distribu- 
tion of heavier and lighter parts must be nullified. 

2. General Effects of Tidal Action in Planetary Life. 
Heretofore in discussing the vicissitudes of nebular masses 
disengaged from primitive nebuhi? by a process of annula- 

* The centre of gravity between the earth and moon is only 2,963 miles 
from the earth's centre. 



TIDAL ACTIOK IN PLANETARY HISTORY. 231 

tion, I have had occasion to direct attention, in a general 
way, to the effects of tidal action both as resulting di- 
rectly from attractions and also from differential centrifu- 
gal tendencies. In the early history of planetary bodies 
tidal actions acquire a remarkable degree of importance. 
I desire, therefore, in entering on a recital of the events 
of primitive planetary history, to explain preliminarily, 
the general mode of reaction of tidal masses. I refer here 
to actions resulting from the existence of tides. 

I have stated that all bodies are susceptible of some 
degree of tidal deformation. The character of the tidal 
effect depends, under a given tidal action, on the facility 
with which the parts tidally moved change their relative 
positions, and, upon a rotating spheroid, the promptness 
with which they respond to the tidal solicitation. These 
conditions concern the height of the tide and its position 
in reference to the tide-producing body. In a perfect 
fluid the height of the tide will be determined only by the 
general law of sphericity; and the apex of the tide will be 
on the shortest line joining the centres of gravity of the 
two bodies. In matter possessed of any degree of vis- 
cosity, the height of the tide will be less than in a perfect 
fluid, and the position of the tide will be somewhat ahead 
of the zenith position of the tide-producing body Viewed 
in reference to time of culmination of the tide-producer, 
the tide therefore lags behind. In a S3^stem, like our solar 
system, where the prevailing motions are from west to 
east, the crest of the tide will be to the east of the zenith 
position of the tide-producing body. In other words, to 
an observer at the apex of the tide, the tide-producing 
body will have passed the zenith. Thus, if O and C be the 
centres of the two bodies concerned, and the body O is 
rotating in the direction of the arrow, then the apex of 
the tide, B, will have passed the point A, under the zenith 
of the tide-producing body C, and will be to the east of 



232 



A COOLING PLANET. 




Fig. 41.— Illustrating a Lagging Tide. 

A by the angular distance BOA. This circumstance, 
due to the viscosity of the body O, gives rise to some very 
interesting deductions. These I will now endeavor to 
make plain. 

(1.) The lagging of the tide tends to a retardation of 
the rotary motion of the tide-hearing hody. — A simple 
inspection of the figure suffices to show that the attrac- 
tion of C upon the tidal protuberance at B must tend to 
draw B around toward A. It is true that attraction is 
exerted similarly by C upon the tidal protuberance at D; 
but the influence exerted upon the centre is greater, and 
the effect of this is a relative movement of D backward. 
To make this plainer we may conceive the anti-tide caused 
by an attraction from the opposite direction, CO; then it 
is evident that the tangential component of this attrac- 
tion, exerted at D, will tend to rotate the spheroid in a 
direction contrary to the arrow. But as B and D are con- 
strained to the surface of the spheroid, the tendency of 
those two points is to bring the prolate^ axis BD into 
coincidence with the line CO, passing through the centres 
of gravity of the tide bearer and tide-producer, that is, 
the lagging of the tide results in a force which opposes 
the rotation of the bodv O.* 



* The horizontal component of the attraction which tends to move B toward 
A may be represented by the tangent BE, Figure 41. Then by the principle of 
the parallelogram of forces we may readily deduce a rough general expression 



TIDAL ACTION IN PLANETARY HISTORY. 233 

This cause of retardation must be set down as real, and 
in the actual constitution of matter, as universal as the 
existence of tides. But now the viscosity of matter comes 
into action in another way. The tide-bearer not being 
rigid, the retarding effect is not fully experienced. The 
protuberant mass at B tends to slide over the bodily 
mass^ and to undergo a translation toward A. The 
amount of actual translation will be inversely as the 
coefficient of viscosity. In a highly viscous mass the 
motion of translation will be but slight, and the protuber- 
ance will yield only as it can draw the whole body around 
with it, or a little more than this. In a highly fluid mass 
the protuberance will yield more readily, the translatory 
movement will be greater for the same lagging, but, on 
the other hand, the lagging will be less, and the horizontal 
component of the tidal force will be diminished also. 

In the case where the tide-bearer is internally more 
rigid than near the surface, or has parts more rigid, 
against which the translated tidal swell may strike, the 
retarding influence assumes more characteristically the 
nature of frictional action. This action must exist when- 
ever any of the moving parts yield more readily than 
other parts in juxtaposition with them. Retardation 
through frictional action presents the most intelligible 

for this component. For, in all cases where the angle BOA=ais small, the 
distance A E is relatively inconsiderable, and C E may be taken as the distance 
of the tide-producer from the surface of the tide-bearer, and O B may be taken 
as the mean radius of the latter. Then, if e=B C E, the angle at the tide-pro- 
ducer subtended by the tangent B E, we shall have in the triangle B O C, 
. „ . BO 

Sm = Sin a :=;-:• 

B C 

Also, in the triangle C B E, 

B E : B C :: sin <J : sin B E C=sin (90° -f a)=cos a, 

.•.BE = BC.^Hi-^ 
cos a 

In this expression B C represents the whole attraction upon B, and B E, its 

horizontal component, or the value of the force acting against the rotation of 

the tide-producer. Putting F for the former and substituting the value of sin 9. 

BE=F?-^tana. 



234 A COOLING PLAITET. 

case where a film like the ocean covers a nucleus rela- 
tively solid which rises above the surface of the film in 
certain regions, presenting shallows and fixed resistances 
to the tidal movements of the film. The mere vertical 
rise and fall of the tides will, in such case, establish cur- 
rents, the initial impulse of which is toward the crest of 
the tide from both directions, but which, from the config- 
uration of the solid resistances, may be deflected in any 
assignable direction. While these currents must exert 
important erosive agency, it is not these which develop 
the friction that tends to retard the rotation of the tide- 
bearer. These currents may, indeed, act in all directions. 
It is the translatory movement of the tide which deter- 
mines a balance of action in the direction of the transla- 
tion; that is, in our system, toward the west. Thus, the 
eastern borders of the resistances should receive somewhat 
severer action than the western. While, however^ all these 
actions and movements are real, they are very minute, and 
can only become of cosmical importance when their results 
accumulate through secular periods. 

In consequence of the retral translation of the tidal 
mass, its position will not be accurately at B, the point 
determined by the viscosity of the tide-bearer, but at 
some point between B and A. The actual tide will occur, 
therefore, a little sooner than might be calculated on the 
basis of viscosity alone. There ought to be thus a slight 
anticipation of the tide. 

One point more. The apex of the tidal swell, but for 
the lagging here under consideration, would be exactly 
beneath the tide-producer. But. in consequence of the 
lagging, the tidal apex is developed some distance to the 
east of the zenith. The point which had been beneath 
the zenith has been carried around by the rotation of the 
tide-bearer. It has been carried around on the equator or 
a parallel of latitude. For the present explanation let us 



TIDAL ACTION IN PLANETARY HISTORY. 235 

suppose the tidal crest to lie under the equator. The 
tide- producer acts upon the protuberant mass from a posi- 
tion a little further west. There are two reasons now 
why the greatest translatory effect should be produced at 
the apex on the equator. Fh'st, that part of the tidal 
swell is nearer the tide-producing body; second, the apex 
being more elevated than the portions lying to the north 
and south, must be more susceptible to the attraction 
exerted upon it. The tidal action is more transverse, and 
the horizontal component is greater. The consequence is 
that the apical portion of the tidal swell must recede 
westward more than the portions to the north and south. 
If, therefore, the meridian passing over the apex of the 
tidal swell at any moment could be fixed to the receding 
surface, it would be broken at the equator into two curves 
inclined to the meridian, and presenting their convexities 
toward the east. The equatorial portion would be borne 
westward m_ore than the other portions. This curious and 
interesting result, first made known by Mr. G. H. Darwin, 
will be hereafter applied to the case of the earth. 

In Figure 42 I have attempted to illustrate more fully 
the consequences of a lagging tide, as far as explained, 
and also other consequences remaining to be noticed. 
Here we have a perspective view of a planetary spheroid 
or tide-bearer, having its axis N S inclined to the plane of 
the orbit O M, in which is moving a moon or tide-producer. 
The direction of the axial and orbital movements is shown 
by the arrows. The broken and dotted lines in the view 
of the planet represent parts on the invisible hemisphere. 
N S is the axis of rotation ; E E E E is the equator; L L L L 
is the great circle of intersection of the plane of the orbit 
O M with the surface of the planet. It cuts the equator 
at two opposite points, X, X. C C C C is a parallel or 
small circle tangent to the last mentioned at m. Other 
small circles are drawn, and also several meridians, for the 



236 



A COOLING PLAN'ET. 




FiCrUKE 42.— Illustrating the Skcllai; Effects of Tides in a 
Rotating Viscous Spheroib. 

N and S are the poles of the spheroid. 

E E E E, the equator. 

C CC C, a small circle, in north latitude, parallel with the equator and tangent to 

L L L L at 7)2. 
P P P P, a small circle, in south latitude, parallel with the equator and tangent to 

L L L L at W. 



TIDAL AOTION^ JJ^ PLANETARY HISTORY. 237 

purpose of giving intelligibility to the diagram. We are 
under the necessity of placing the tide-producer M, dis- 
proportionately near the tide-bearer; but this only exag- 
gerates the quantities which it is desired to bring into 
notice, and hence is a real help. 

Now the tide-producer is supposed to be in the zenith 
over m, and accordingly a tidal effect is progressing at m. 
But this effect, in consequence of viscosity, does not reach 
its culmination until the rotation of the planet has trans- 
ferred the point m to ^, and t, therefore, is the place of 
high tide. Suppose M to be the tide-producing body at 
this juncture. Then a tidal protuberance exists on the 
meridian passing through t, somewhat to the east of the 
zenith position of M, and the attraction of M exerted upon 
t tends to rotate the planet backward, around the axis N S, 
toward m. The amount of this tendency is the retarding 
effect of the lagging tide. The apex of the anti-tide is at 
t' instead of 77i\ and the lagging of the anti-tide brings it 
to a position where the attraction of the theoretical anti- 
tide-producer tends to draw it retfally from t' toward in', 
and thus as before, to retard the rotational motion of the 
planet. 

The attraction of the tide-producer exerted upon t pro- 
duces a virtual retral motion which we may assume repre- 
sented by tt^. The distance tt^^is therefore the anticipation 

LL L L, intersection with the spheroid's surface of the plane of the orbit of the 

tide-producer. 
XX. diameter joining intersections of equator and LLLL. 
M, tide-producer, assumed to be vertically overm. 
O M, portion of the orbit of the tide-producer, 

m, point under M, and the apex of the tide in case of perfect fluidity. 
t, apex of the tide as determined by lagging from m to /. 
<i,actnarapex of the tide, as resulting from lagging and from retral slipping from 

Uo^i. 
m\t\ / 1', corresponding points of the anti-tide. 
Mr, acceleration of the tide-producer caused by the attraction of the tide from 

t, or more exactly from ti . 
M'r, recession of the tide-producer caused by its acceleration and increased 

centrifugal tendency. 



238 A COOLTN'G PLANET. 

of the tide, or the amount by which it occurs sooner than 
might be expected when the calculation of its position is 
based simply on the amount of lagging due to the viscosity. 
It will be borne in mind that the retral pull may be con- 
ceived as developing in part an actual retardation of the 
planetary spheroid, and in part a retral translation of a 
portion of the more fluid film upon the surface. The rela- 
tive amounts of retardation of the whole body, and retar- 
dation or retral translation of the surface, will be deter- 
mined by the viscosity of the film and its opportunities 
for action against fixed or relatively fixed parts of the 
included nucleus. 

Supposing a film more fluid than the nucleus, and a tide- 
producer M, acting on a tidal swell whose crest is at t, 
then obviously, the greatest amount of retral movement 
will be produced at t, while north and south of t the retral 
movement will be less, both because of the greater dis- 
tance of the attracting body and of the less height of the 
tide. 

As the tide-producer moves in its orbit it reaches a 
point directly over the node X. In this position the re- 
tarding factor of the attraction is more effective than 
before, and the linear retral motion of the surface-film will 
be greater, since the retarding force is applied at a greater 
distance from the axis. When, at a subsequent epoch, 
the tide-producer is over m' , and the tide is at t' , then the 
retarding and translatory effects become precisely as at m 
and t. Hence the retarding and translatory effects attain 
a maximum when the tide-producer is nearly over the 
planetary equator, and dnninish thence during the northern 
and southern declinations. That is to say, considering the 
aggregate translatory effects during an orbital revolution 
of the tide-producer, the retral movement will be greatest 
at the equator and will diminish thence toward the poles. 
The equatorial regions will suffer a greater westward shift- 



/ 



TIDAL ACTION IN PLANETARY HISTORY. 



239 



ing of longitude than regions farther north and south; so 
that lines once meridional will eventually present an in- 
clined double convexity eastward, with north-eastward 
trends north of the equator, and south-eastward trends 
south of the equator. 

As the lagging of the tide results from the viscosity of 
the tidally disturbed matter, the amount of the lagging 
becomes a measure of the viscosity. But, that it may be 
accurately such measure, correction must be made for the 
retral slipping of the superficial film in the latitude where 
the apex of the tide is situated. 

In the case of a tide-bearer constituted of a nucleus of 
higher viscosity, and an enveloping film of lower, each 
part will develop its own tidal protuberance, and that of 
the nucleus will lag more than that of the film. This is 
shown in the adjacent figure, where A B is the prolate 




Fig. 43.— Discordant Tides of Nucleus and Film. 



axis of the film, and C D the prolate axis of the nucleus. 
It is to be remarked, in view of this state of things, that 
the problem of the rigidity of the nucleus as depending on 
the measured depth of the tide A «, must take account of 
the fact that a is not the point at which the nuclear tide is 
developed. 

(2.) The lagging of the tide produces a slow reces- 
sion of the tide-2yrodiicing body. — Recurring to Figure 41, 
let H I represent a portion of the orbit of a tide-producer 



240 A COOLING PLAlfET. 

moving in the direction of the arrow. This, according to 
the process of world-making which we here maintain, will 
be in the same direction as the rotation of the tide-bearer. 
The apex of the tide will be, therefore, at B, in advance 
of the position of the tide-producer, and an attraction will 
be exerted by the tidal mass upon C, in the direction C B. 
While the greater part of this attraction coincides with 
the mean centripetal force drawing C toward O, a small 
component of it, as the diagram shows, tends to accelerate 
the motion of C in the direction C I. But C was supposed 
to be moving with such orbital velocity as held it balanced 
between centripetal and centrifugal forces, and if now that 
velocity is increased, the centrifugal tendency is increased, 
and C tends to move in the direction of the tangent C G. 
That is, its distance from O is increased. But now, re- 
moved to a greater distance, the centripetal force is dimin- 
ished, and the tide-producer moves in such an orbit that 
its diminished centrifugal tendency again equilibrates the 
centripetal tendency. Thus there results the apparent 
anomaly that an accelerati(^ of the body in its orbit leads 
tCLTetardation. To put the matter in another light, let us 
consider that while the total attraction of the body O is 
the same with or without the tide, one part of it when the 
tide exists, is exerted in the direction C B instead of C O, 
and develops the tangential tendency C G"; while the re- 
maining part exerted in the direction C O is less than the 
centripetal force exerted by the body when not tidally dis- 
torted. That is, the proper centripetal force is diminished. 
But since the orbital velocity of C is the resultant of cen- 
trifugal and centripetal components, it will be diminished 
by the diminution of the centripetal component. Diminu- 
tion of orbital velocity diminishes in turn the centrifugal 
tendency. So the body C, in being drawn along the tan- 
gent C G. and getting a little outside of its orbit, experi- 
ences diminution of centripetal force, orbital velocity and 



TIDAL ACTION^ IN PLANETARY HISTORY 241 

centrifugal force. In other words, it revolves at a slightly 
greater distance from the centre O, and with a diminished 
linear and angular velocity.* The principle is precisely 
the converse of that under which a resisting medium, in 
opposing the orbital motion of a body, determines an ac- 
celeration of velocity, and motion in a smaller orbit. 

This reaction of the tide may perhaps be more thor- 
oughly understood by the use of the general diagram. 
Figure 42. Here as before, the crest of the tide is at t^ 
when the tide-producer is in the zenith at m, and the 
action exerted from t^ tends to accelerate M in the direc- 
tion of r; but acceleration causes M to depart from its 
orbit in the direction of the tangent M M', and thus, as 
before, orbital retardation is the ulterior result. The same 
action takes place at whatever point along the great circle 
L L L L the tide may exist during the movement of M for- 
ward in its orbit. 

A very high state of viscosity may result in retardation 
instead of acceleration of the tide-producer in its orbit. 
Let the annexed diagram be a projection on the plane of 
the planet's equator. Then when the lagging of the tide 
amounts to 90°, as at t^, the anti-tide at t\ exerts an at- 
traction on M which nearly neutralizes the attraction of 
the tide. At some distance east of ^j, as at ^2, the attrac- 
tion exerted upon M by the anti-tide, ^'g, exceeds the 
attraction exerted by the tide. The excess of action of 
the anti-tide results in a retardation of M; it is, therefore^ 
drawn by centripetal action nearer to the planet, and its 
velocity is accelerated. A very high state of viscosity 

* This ca.«e illustrates the Interesting fact that the influence exerted hy an 
attracting body must depend, in certain positions, upon its figure. If there were 
no lagging of the tide the motion of the tide-producer would not be affected ; 
and if the lagging were just 90°, the influence of the anti-tide would neutralize 
that of the tide. So the equatorial protuberance of an oblate spheroid must 
exert an influence on the motion of a body revolving around it, except when the 
body is in the plane of the protuberance, or exactly in the line of the axis pro- 
duced—a relation which never exists in our system. 
16 



242 



A cooli:n^g pla^^et. 




Fig. 44.— Varting Reaction Resulting from Vakting Viscosity. 



exists at the surfaces of plaiietan^ bodies when passing 
from the fluid to the solid state, but whether it ever pro- 
duces sufficient tidal lagging to work a retardation of a 
satellite is unknown. Undoubtedly the more prolonged 
and older fluidic condition, accompanied by accelerative 
lagging of tide, impresses more important results on the 
life- history of satellites. 

This direct retardative result proceeds from the influ- 
ence of excessive viscosity in any state of inclination of 
the orbit and the planetary equator. The result will be 
reached also, with a low^er degree of viscosity, in propor- 
tion as this inclination is increased; because the greater 
the inclination the sooner the lagging tide is carried by 
the planet's rotation around to a point in the rear of the 
radius vector^ of the tide-producer. This will be under- 
stood from the general diagram, Figure 42, by conceiving 
the great circle L L L L to have such obliquity as to be 
tangent to the small circles around the poles N and S. A 
tide inaugurated at any point on this great circle will be 
carried nearly at right angles away from it by the planet's 
rotation, and the tidal culmination may be reached, espe- 
cially if the lagging is great, at such a distance that the 
curvature of the parallel brings the crest of the tide to 



TIDAL ACTION" IN" PLAN^ETARY HISTORY. 243 

the west of the radius vector of the tide-producer. It 
appears, therefore, that as the inclination increases, the 
degree of viscosity which will produce retardation dimin- 
ishes, and when the inclination is 90°, acceleration results 
under all degrees of viscosity, when the tidal crest is in 
the southern hemisphere, while retardation results when it 
is in the northern hemisphere. On the contrary, as the 
inclination diminishes, the degree of viscosity requisite to 
produce retardation increases, and when the inclination is 
zero, the viscosity must be such as to produce a lagging of 
more than 90° of longitude. 

(3.) The lagging of the tide increases the inclination 
of the equator' of the tide-bearer to the orbit of the tide- 
producer. — By reference to the general diagram, Figure 
42, it is seen that an attraction exerted by a body M upon 
a tidal protuberance at t^ imparts not only a tendency of 
the tide-bearer to rotate backward around the axis N S, 
but also a tendency to rotate around the axis X X. In 
other words, the actual motion of the tide-bearer in the 
direction of the pull may be resolved into two rotations 
about the two axes named. The tide-producer is always 
vertically over some point of the great circle L L L L. 
When that point is north of the equator, the rotation of 
the tide-bearer carries the tide north of the plane L L L L, 
and an attraction exerted from that plane must tend to 
bring the tidal crest into the plane; that is, to bring a 
point north of the plane LLLL southward into that 
plane. The effect of this must be to increase the inclina- 
tion of the axis N S toward the axis of the plane LLLL. 
When the apex of the tide is south of the equator, the 
rotation of the tide-bearer carries it south of the plane 
LLLL, and an attraction exerted from that plane must 
tend to bring the tidal crest into the plane; that is, to 
bring a point south of the plane LLLL northward into 
that plane. The effect of this must also tilt the axis of 



24:4 A COOLIXG PLAXET. 

the tide-bearer into a larger inclination to the axis of 
L L L L. In all positions of its orbit, therefore, the tide- 
producer increases the angle formed by the great circles 
E E E E and L L L L. 

Reciprocally, however, the reaction of the tide in all 
positions where the inclination referred to is increased, 
exerts a tendency to move the tide-producer M above or 
below the plane of its orbit. When the tidal crest by 
lagging is carried above that plane, the tide-producer is 
drawn above it. In all that half of its orbit which lies 
north of the equator, the tendency of the lagging tide is 
to keep the tide-producer above the plane of its orbit. In 
all that half of its orbit which lies south of the equator, 
the tendency of the lagging tide is to keep the tide-pro- 
ducer below the plane of its orbit. That is, one-half of 
the orbit is elevated and the other is depressed. The 
inclination of the orbit is changed in reference to a con- 
stant plane; say the fundamental plane of the planetary 
system. 

The action of the tide in increasing the angle between 
the axis N S and the axis of L L L L would not result in a 
steady movement of one pole from the other. The pole 
N would pursue a sinuous course, making one sweep to 
the east and one to the west at each semi-revolution of 
the tide-producing body. Similarh" the path of this body 
would be sinuous — moved twice above its mean position 
and twice below it during each revolution. 

As the viscosity of the tide-bearing medium increases, 
the position of t in Figure 42 moves around farther east 
on the parallel C C C C. At length, with further suppos- 
able increase of viscosity, the amount of lagging becomes 
90°. At this point the increase of obhquity ceases. 
Beyond this point, the effect of lagging is to diminish the 
obliquity. This is more clearly shown, for a particular 
position of the tide-producer, in the annexed diagram, 



TIDAL ACTION IN" PLAJ^-ETARY HISTORY. 



245 




Fig. 45, — Tidal Increase and Diminution 
OF Obliquity. 



Figure 45, where the 
equator and parallels 
and plane of the orbit 
of the tide-producer 
(wi A) are seen, from 
an infinite distance, 
projected in straight 
lines. M is the pro- 
jection of the tide-pro- 
ducer. When the pro- 
jection of the retarda- 
tion is 'm t, the effect of 
attraction toward the 
plane of the orbit rn A, 

is to increase the inclination of the axis N S. When the 
projection of the retardation is mt^, no effect is produced. 
When the projection of the retardation is mt^ or ')nt^, the 
effect of attraction toward the plane ni A is to diminish 
the inclination. The theoretical anti-tide-producer acts 
concurrently, as shown in this diagram. It appears, there- 
fore, that with a high state of viscosity the increase in 
the obliquity may become inl, or even changed to a dimi- 
nution. 

The three classes of tidal reactions thus explained are 
reciprocal. The planetary body exerts a tidal influence 
upon the lunar body as much greater than that experi- 
enced itself, as its mass is greater than that of the lunar 
body; though the height of the tide raised depends also 
on the radius of the lunar body, and the mobility of its 
parts. Since the lunar body must be viewed as always 
more or less viscous, and on our theory, must at some 
stage pass tlirough a semi-fluid state, the lagging of the 
tide borne by this body must tend always to retard its 
rotary motion. This general deduction leads us to some 



246 



A COOLIKCt PLAIn^ET. 



very interesting applications to particular cases, as will 
hereafter be shown. 

The reaction of the lunar tide upon the orbital motion 
of the planet around the common centre of gravity of the 
two bodies, however insignificant in amount, is a sequence 
w^hich is real. Let M, Figure 46, represent a moon, a the 







Fig. A^ — The Tide-Bearer Vieaved as Tide-Producer. 



centre of gravity of a planet, and C the centre of gravity 
between the moon and the planet. The centre of gravity 
a revolves about the centre of gravity C in an orbit a h c. 
On the moon the lagging of the tide brings its apex to t, 
and this lagging tide acts on the centre of gravity a. As 
this action is not in the direction of the radius vector a C, 
the tendency is to accelerate a toward w. This, as before, 
by increasing the centrifugal force increases the distance 
from C to a, and ends in retardation of a in its orbit. As 
the planet and' satellite are always in the same position 
in relation to C, this action exists in all parts of their 
respective orbits. So the tidal retardation of the lunar- 
planetary revolution about the common centre C is the 
sum of the reactions from the lagging tides upon the two 
bodies. 

It \v\\\ be noticed also, that with a high degree of vis- 
cosity, producing a lagging of more tlian 90°, the reaction 
upon a exerted by the anti-tide of the satellite w411 exert a 
retarding influence upon the orbital motion of a. The ac- 



TIDAL ACTIOJ^ 11^ PLANETARY HISTORY. 247 

celerative and retardative influences of planet and satellite 
are, therefore, precisely reciprocal and consentaneous. 

Similarly, it will appear, on a moment's consideration, 
that if the axis of the satellite possesses some degree of 
inclination to the axis of the planet's orbit, such inclination 
will be increased and diminished under the same conditions 
as increase and diminution of the planet's inclination to 
the satellite's orbit. 

This whole subject ought to be contemplated under re- 
lations still more general. Each of the planets stands in 
the tidal relation of a satellite to the sun, and the sun is a 
tide-producing body to each of its planets. The remote- 
ness of the major planets diminishes this reciprocal action, 
perhaps, below the limit of cosmical importance, but, on 
the contrary, tidal actions within nearer limits must possess 
a high degree of importance. The same kind of influence 
which a planet exerts upon a satellite, the sun exerts upon 
the planet itself. That is, the solar tide tends to retard 
the planetary rotation, to retard its angular motion in its 
orbit, and to increase the inclination of its axis to the axis 
of its orbit. The tide upon the sun must tend also to 
draw the planet out of the plane of its orbit, and thus to 
increase the obliquity of that plane to the plane of the 
sun's equator. 

We are thus brought face to face with the striking fact 
that tidal evolution is a suggestive explanation of many of 
those apparent anomalies which have been cited as difficul- 
ties in the nebular theory. Inadequate rotary and orbital 
velocities may be thus explained. Inclinations of axes of 
rotation may have been brought to a higher degree — and 
highest upon those planets most affected by solar tides. 
Even the inclinations of the planetary orbits may have 
been increased by tidal protuberances on a sun rotating with 
some preexisting inclination of its axis. We cannot, how- 
ever, explain all axial and orbital obliquity in this way. 



248 A COOLIXG PLAXET. 

Change in obliquity depends on the antecedent existence 
of some obliquity. With obliquity nil we have conditions 
of equilibrium. There must have been other causes to 
inaugurate the obliquity which tidal influence increases. 
The existence of other causes has been heretofore pointed 
out. (Part II, ch. i, §§ 2-3.) 

3. Tendency to Synchronism of Rotary and Orbital 
Motions. — We may now proceed to trace more specifically 
some necessary deductions from the physical principles 
thus defined. Every planetar^^ body in the solar system 
has always been tidally influenced by every other body in 
the system. We may disregard, however, at present, the 
tidal disturbances excited in the sun, and also the influ- 
ences of the primary planets upon each other. Great im- 
portance, however, must be conceded to three classes of 
tides: First, The influence of primaries upon their 
secondaries. Second, The influence of secondaries upon 
their primaries. Third, The influence of the sun upon 
the planets. The greatest tidal distortion would result 
from the influence of a primary of large mass upon its 
own satellites. The mass of Jupiter being three hundred 
times that of the earth, and his inner satellite being but 
little more remote than our moon from the earth, the tidal 
influence of Jupiter upon his inner satellite should be, for 
these reasons, about three hundred times as great as the 
influence of the earth upon the moon. But since this 
satellite has about the diameter of the moon, with less 
than half its mass, the tidal influence of Jupiter would 
become still more enormous. The tidal influence of the 
earth upon the moon, so far as due to relative mass, should 
be about eighty times as great as that of the moon upon 
the earth. The enormous tides raised upon the satellites 
while in a primitive aeriform, fluid or semi-fluid condition 
must have exerted a most important influence upon their 
development. Confining our attention to the retarding 



TIDAL ACTION IN" PLAN^ETARY HISTORY. 249 

effect, this must have had almost a controlling power over 
their axial rotations. It may even be doubted whether the 
whole process of shrinkage after the attainment of a semi- 
fluid state, and the consequent diminished tendency to ac- 
celerated rotation, has been sufficient to overcome the 
tidal influence of the primary in any single instance, so as 
to establish for any epoch an angular motion more rapid 
than the satellite's orbital motion. As the moon turns 
always the same side toward the earth, it is reasonable to 
infer that this condition has been produced by the tidal in- 
fluence exerted chiefly by the earth. It seems probable, 
also, that the condition was assumed at an early period in 
the moon's history, even if a non-synchronous rotation 
had once been established during an earlier aeriform period 
when freer mobility of parts gave the moon somewhat the 
character of a perfect fluid, in which tidal lagging would 
not take place. So far as we can judge from observation, 
other satellites have attained a similar state of synchronistic 
motions; and this is certainly in accordance with our 
reasoning. 

A reciprocal though greatly inferior influence is exerted, 
or has been exerted, by each satellite upon its primary. 
During the plastic condition of the primary, the deforma- 
tive tide must lag, and a retarding effect must result. 
Each planet has been strained to desist from its rapid 
rotation, and present constantly the same side toward its 
most powerful satellite. Without the least doubt this 
influence, continued through millions of years, has mate- 
rially retarded the rotary motions of the planets.* Those 

*Kant, the great thinker, whose sagacity can scarce!}' be too much re- 
spected, was the first to make note of these reciprocal tidal actions on the 
earth and moon. See his prize essay, presented in 1754 to the Berlin Academy 
of Sciences, entitled: Untersuchung der Frage^ ob die Erdein ihrer Umdrehung 
um die Achse, wodurch sie die Abwechselung des Tages tmd der Nacht hervor- 
bnngt, einige Verdnderung seit den ersten Zeiten Hires Ursprunges erlitten habe, 
und woraus man sich ihrer versichern konne. 



250 A COOLTXG PLANET. 

planets would be most retarded whose masses sustain 
lowest relations to the masses of their satellites — allow- 
ance being made also for distances. The earth, and possibly 
Mars, should have departed most from their primitive 
axial velocities ; Jupiter and the exterior planets least. 
But Venus and Mercury being unprovided with satellites, 
have been unaffected by their influence. Observation has 
not certainly shown what is their actual rate of rotation. 

The tidal influence exerted by the satellites upon the 
planets would be reinforced by the sun's influence upon 
them. At the distance of the earth, the solar tidal effi- 
ciency is two-fifths that of the moon upon the earth. At 
the distance of Venus the solar tidal efficiency is one and 
two-fifths times as great as at the earth ; which gives 
at Venus a solar tide two-thirds as great as the lunar tide 
upon the earth. At Mercury the solar tidal efficiency is 
17.4:4 times as great as upon the earth, which is 6.976 
times as great as our lunar tide. These two planets, 
therefore, while exempt from the retarding influence of 
satellites, have suffered very important retarding influ- 
ences exerted by the sun. It would not be a stretch of 
probability to conclude that Mercury, at least, has attained 
already a state of synchronistic axial and orbital motions, 
even if such state has not existed from the gaseous epoch 
of the planet's evolution. 

At a later period in a planet's career, after approxi- 
mate rigidity has diminished greath^ the retarding influ- 
ence of deformative tides, the tidal disturbance of the 
fluids on their surfaces maintains a frictional retardative 
action which continues the tendency to synchronistic mo- 
tions. Whenever a planetary surface becomes covered 
with a film of water, interrupted in places by protruding 
portions of the solid nucleus, then all tidal movements 
of the water along the shores of islands and continents, 
and over bottoms not beneath the influence of such dis- 



TIDAL ACTIOJs^ IN PLAKETARY HISTORY. 251 

turbances, is met by resistances which tend to destroy the 
motions. As tlie resultant of all the tidal motions is 
toward the west, the rotary motion of the tide-bearer is 
continually diminished, and continuall}^ approaches syn- 
chronism with the orbital motion of the tide-producer. 
Thus the earth is tending- to settle into such a rate of 
rotation that one side will always be turned toward the 
moon. After this condition shall have been reached, the 
solar tide will further retard its rotation toward the limit 
where the same side will be turned constantly toward the 
sun. Meantime, however, after a planet's rotation, by this 
influence, becomes slower than the orbital revolution of its 
satellite, a lunar tide will spring up again, lagging behind 
the satellite, and tending to accelerate the planet's rota- 
tion. If the lunar tide should now retain all its former 
magnitude, the satellite would prevail over the sun, and 
prevent final synchronism with the sun. But the satellite, 
as has been explained, has receded from its planet, and its 
tide has diminished as the cube of the distance increased. 
Besides, the amount of lagging now is less, since the sat- 
ellite passes the planet's meridians more slowly. Thus 
the power of the satellite may not be able to cope with 
that of the sun, and the planet may ultimately turn the 
same side continually toward the sun. 

Whenever a body is brought to turn the same side con- 
stantly toward a tide-producer, then some important 
changes must take place in the distribution of the fluids 
upon its surface. Not only will a state of permanent 
bodily deformation result, and thus all mechanical devel- 
opment of internal heat be arrested, but now all the fluids 
will dispose themselves on the remoter side of the body. 
Thus all the water would be displaced from the nearer 
pole of the prolate axis, and accumulated about the 
remoter one. The atmosphere would also be similarly 
distributed. No body thus fixed in its position should 



252 A COOLIXG PLAXET. 

therefore present any seas, or perhaps atmosphere, to the 
view of an observer placed on the tide-producer which 
controls its rotation. This supposes, however, that these 
fluids exist in nearly the same proportion to the body as 
on the earth. But we shall discover hereafter another 
cause of the disappearance of water and atmosphere. 

4. Predetermination of Sitb-meridlonal Trends. — In 
the early incrustive periods of a planet's existence, the 
tidal disturbance would determine some permanent fea- 
tures of the surface. It seems to me that some meridio- 
nal disposition of the structure of the crust would arise 
without the intervention of the retral translatory motion 
already considered in its general features. The tidal wave 
would be an immense swell of the liquid portion stretching 
meridionally f rom high northern to high southern latitudes. 
It Avould indeed, have a corresponding breadth from east 
to west. Its progressive changes of position, however, 
would be across the meridians. The successiveness of 
similar tidal conditions and effects would extend from east 
to west. This would be true of parallels north and south 
of the zenith positions of the tide-producing body, as well 
as of those experiencing the maximum tidal influence. 
Simultaneousness of tidal conditions and effects would 
extend meridionally. The progressive westward changes 
in the position of the swell must determine arrangements 
of the rising and sinking fragments having relation to 
the direction of the progress. Parts along the same me- 
ridian would sustain identical relations to the direction of 
the progress, and receive an identical and simultaneous 
impress. Though the next meridian would be immedi- 
ately visited by the same action, it would be the simulta- 
neous results rather than the successive ones, w hich would 
determine zones of homogeneous structure or similar con- 
dition, like the lines of growth over the surface of a 
sea-shell. Accessory causes would be joined to these influ- 



TIDAL ACTION IX PLANETARY HISTORY. 253 

ences. Whatever effects might result from the conjunc- 
tion of any casual influences with tidal action, would arise 
simultaneously along meridional lines more or less ex- 
tended.* Such casual influences might originate in storms 
or special conditions of the crust. It is reasonable to 
suppose, therefore, that the tides would impress some 
characteristics of surface meridionally disposed. 

But there is a stronger reason for supposing this, as 
has been shown. The inertia of the tidal mass and the 
friction of moving parts upon each other would cause the 
summit of the swell to linger somewhat behind the me- 
ridian passage of the tide-producing body. This body 
would therefore exert constantly some force of displace- 
ment tending to give the tidal mass a slight motion of 
translation opposite to the direction of the rotation of the 
tide-bearing body. Whatever translatory motion of the 
tide wave might result — whatever pressure might be 
exerted by a tendency toward translatory motion, would 
be an effect which, combining with the casual influences, 
would still more distinctly impress meridional features 
upon the constitution and structure of the solidifying 
crust. The tendency to translatory motion may be very 
slight; the aggregate impression of all these causes may 
be slight; but if these are real physical causes they may 
aggregate enough to turn a balance of conditions, and 
leave on the surface of the solidified planet some record 
of their existence. 

In the early incrustive stages this tide would not only 
break the forming crust into a mass of angular and after- 
w^ard rounded fragments, but would initiate some ten- 
dency to westward motion for certain distances. When 

* Transmeridional features might indeed be created by any influence 
changing its point of application in the direction of the tidal motion, as we find 
upon the exterior of a sea-shell lines of structure transverse to the lines of 
growth, and sustaining relations to causes which move in the direction of the 
growth. 



^54 A COOLIis^G FLAXET. 

this tendency should be finally overcome by aggregated 
resistances, the fragments would be left in long ranges 
meridionall}^ disposed, which, though incomparably less 
pronounced, might be compared to the windrows of ice- 
blocks piled along the shore by the swell upon the surface 
of one of the great lakes. Thus a certain predisposition 
to meridional trends would be induced. 

At a later stage, when a continuous floe-like crust 
should have come into existence, the same tidal swell would 
raise the crust in broad billows which would continually 
change their position westward on new belts of crust. 
Whatever action should be exerted — whatever effects 
produced, they would range meridionally, and this effect 
would be reinforced by the tangential component of the 
tidal action. Thus the crust would come into existence 
with ingrained meridional features in its structure, and 
with predetermined aptitudes to assume new features hav- 
ing the same general trend. If, subsequently, any cause 
should necessitate the development of wrinkles in the 
crust, the earliest ones must naturally assume meridional 
trends. Such trends once inaugurated, others parallel 
with them would, by a double necessity, come into exist- 
ence if the wrinkling process should continue. Thus all 
the primitive wrinkles should, under a general law, ex- 
hibit trends across the parallels. At later periods, after 
an advanced differentiation of the planetary surface, sec- 
ondary causes might induce wrinkles and folds of the crust 
trending in other directions. Great interest arises in the 
application of these principles to the case of the earth. 

In these statements concerning the inauguration of 
meridional trends I have said nothing concerning the dif- 
ferential retrograde slipping of the equatorial regions 
and those situated to the north and south of the equator. 
It will be borne in mind, however, that the tangential com- 
ponent of the tidal force is most effective at the crest of 



TIDAL ACTIOi^ IN PLANETAKY HISTORY. 255 

the tide. It follows, therefore, that the structural features 
thus far referred to as meridional would tend to assume, 
north of the equator, a trend somewhat northeasterly, and 
south of the equator a trend somewhat southeasterly.* 

5. Outflow of Molten Matter. — The tidal elevation 
and depression of the planetary crust would not only 
cause extensive fractures, but would furnish occasion- for 
the outflow of molten matter through the vents. It is 
certain that the effort of the underlying liquid to rise 
higher than the partially rigid crust would rise, would 
cause the fluid to escape through any fractures which 
might exist, and overflow the surrounding surface. This 
fluid solidifying around the border, would eventually build 
up a crater-like elevation of any assignable magnitude. 
In later periods, upon a planet supplied with the condi- 
tions of extensive denudation, these crateriform emi- 
nences might disappear; while on a planet not supplied 
with the conditions of denudation, they might remain 
indefinitely. These principles have a very important ap- 
plication in the case of the moon. 

6. Crushing Effects of Tidal Deformation. — Planet- 
ary tides would never cease to be felt. A planet would 
never become so solid as not to yield to an influence as 
powerful, for instance, as that which the moon exerts 
upon the earth. The tide would be a perpetually shifting 
deformation of the solid parts of the planet. This must 
necessarily be accompanied by extensive molecular dis- 

* Although the establishment of primitive meridional trends was worked 
out by me independentljs I am indebted to Mr. G. H. Darwin for the suggestion 
that these trends would make an angle with the meridian. See his highly in- 
teresting memoir on Problems Connected with the Tides of a Viscous Spheroid, 
read before the Royal Society of London, December 19, 1S78. Phil. Trans., Pt. 
II, 1879. Mr. Darwin shows that each point of the jjlanet's surface moves from 
east to west with a linear velocity proportional to the cube of the distance from 
the axis, and the parts north of the equator change their longitude /row west to 
east relatively to the equator, at a rate proportional to the square of the sine of 
the latitude. 



256 A COOLIXG PLACET. 

placement. It is, in effect, a crushing agency, and the 
consequence must be the development of an enormous 
amount of heat. It would appear, therefore, that even 
after a planet should have been chilled to its centre, tidal 
deformation must continue to produce the phenomena of 
internal heat. Until the time should arrive when the same 
side is turned continually toward the tide-producing body, 
the progressive transfer of the tidal swell w^ould produce 
at any given point not too near the poles, periodical 
movements of the planetary crust. The daily effects of 
these disturbances might in part be stored up in the form 
of strains and tensions which, modified and probably in- 
tensified by general shrinkage, would, at longer and at 
irregular intervals, become too great for the planetary 
structure to endure, and would thus eventuate in sudden 
and violent uplifts or collapses, and at times, in the open- 
ing of vents for the escape of internal heated substances. 
These violent strains and sudden movements would be 
most likely to occur after the attainment of a high state 
of rigidity in the crust, and the formation of permanent 
inequalities of considerable magnitude. 

7. Marine Tides in the Early History of a Planet. — 
The marine tides produced in the early history of a planet 
must sustain important cosmogonic relations. It has been 
already stated that the friction of marine tides upon shores 
and the bottom of shoals must tend to diminish the velo- 
city of a planet's axial rotation. It has also been main- 
tained that a similar result must ensue from the tidal 
effects produced in a viscid or even a solid planet, if not 
possessed of complete rigidity. As this cause of retarda- 
tion is operative in every planet subjected to tidal action, 
it is supposable that the rotational velocity of any particu- 
lar planet was higher in former periods than at present. 
As the rate of retardation must have been inversely as the 
ratio of the masses of the planet and its tide-producing 



TIDAL ACTIOX 1:N^ PLANETARY HISTORY. 257 

satellite or satellites (as well as inversely as the cube of 
the distance) it may be inferred that smaller planets, other 
things being equal, have suffered greater retardation than 
larger ones. The more rapid rotation of the larger planets 
of our system is in accord with this view. 

If the rotational velocity of the earth is thus in process 
of diminution, from what rate of velocity did the diminu- 
tion begin? According to the theory set forth in this 
work, the earth's rotary velocity was once such that the 
centrifugal tendency on the equator was equal to the force 
of central gravitation, and at that time the matter of the 
moon separated as a nebulous ring. An equilibrium of 
centripetal and centrifugal tendencies would be reached 
at the present terrestrial equator if the earth's rotation 
were increased seventeen times.* But in the nebulous 
condition in which annulation is supposed to have taken 
place, the radius of the earth's mass was much greater 
than at present, and hence the physical conditions of 
annulation would have been supplied by a much slower 
rate of rotation. The present radius of the moon's orbit 
cannot be assumed as the earth's radius at the epoch of 
annulation, since, as has been shown, the moon is now in 
progress of recession from the earth, and must have been 
so ever since the commencement of lunar tides on the 
earth's surface. Lunar tides must have begun as soon as 
the moon acquired a separate existence in such form that 

* Let / = present centrifugal tendency at the equator, the time of rotation 
being t. 

f— centrifugal tendency when the time of rotation is t'. 
g = present force of gravity at the equator. 
g'= force of gravity in the absence of any rotation. 
Then, since, in the same sphere, the centrifugal tendency is inversely as 
the square of the time of rotation, 

sinye /-' is to become equal to g'. But the physical constant 

/ = 0.111255, and g'^ 32.200795, 
whence f/^= .003455 f^^ ^^rf i^ nearly, 

and t^^ .05878 t = yV < "early = 1.41138 hours. 

17 



258 A COOLIXG PLAisET. 

its attraction was not exerted equally and simultaneously 
upon all meridians of the equatorial belt. A ring having 
its mass uniformly distributed would not produce a proper 
tide, though it would produce an annular elevation around 
the earth. But as soon as the centre of mass in the ring 
should cease to coincide with the geometrical centre, a 
tidal action would begin ; and this would increase until 
the annulus should have become a spheroid. It seems 
entirely probable on physical grounds, that definite tidal 
action began, and that even the lunar spheroid began its 
work, when the lunar mass was much nearer the eartli 
than at present. Guided by physical laws the geognostic 
student must, therefore, bear in mind the probability of 
some extraordinary tidal action in the early periods of the 
earth's history. 

Mr. G. H. Darwin has developed in this connection 
some views of novel originality and interest.* Proceed- 

* The following are Mr. Darwin's principal memoirs : 

1. On the Bodily Tides of Viscous Spheroids. Proc. Eoy. Soc, May 23, 
1878; abstract, Nature, xviii, 265-6, July 4, 1878. 

2. On the Precession of a Viscous Spheroid. British Assoc, Dnblin Meet- 
ing, 1878; abstract, Nature, xviii, 580-2. 

3. On the Precession of a Viscous Si^heroid, and on the Remote History of 
the Earth (with the following; : 

4. Problems Connected ivith the Tides of a Viscous Spheroid. Proc. Key. 
Soc, Dec. 19, 1878 (Phil. Trans., Pt. 2, 1879); abstract, Nature, xix, 242-3, Jan. 
30, 1879. 

5. On the Secular Effects of Tided Friction. Proc. Boy. Soc, June 19, 1879; 
abstract. Nature, xx, 246-7, July 10, 1879. 

6. On the Secular Changes in the Elements of the Orbit of a Satellite Revolv- 
ing about a Planet Distorted by Tides. Proc Roy. Soc, Dec. 18, 1880 {Phil. 
Trans., Pt. 2, 1880, p. 731); abstract. Nature, xxi, 235-7, Jan. 8, 1880, erratum, 
p. 276. 

7. On the Tidal Friction of a Planet Attended by Several Satellites and on the 
Evolution of the Solar System. Proc. Eoy. Soc. Jan. 20, 1881 ; abstract. Nature, 
xxiii, 389-90. 

8. On the Stresses Caused in the Intenor of the Earth by the Weight of 
Continents and Mountains. Proc. Roy. Soc, June 16, 1881: ahstract, Nature, 
xxi V, 231, July 7, 1881. 

9. On the Geological Importance of the Tides. Nature, xxv, 213-4, Jali. 5. 
1882. 

10. The Movements of Jupiter's Atmosphere, Nature, xxx, 360-1, Feb. 16, 
1882. 



TIDAL ACTION" IN PLAJ^ETARY HISTORY. 259 

ing from the starting point already determined by the 
researches of Ferrel (1853), Helmholtz, Purser, Sir Will- 
iam Thomson and Delaunay, Mr. Darwin has attempted to 
retrace the course of tidal retardation of the earth's rotary 
motion through the long geons of the past. Having shown 
that the recession of the moon must keep pace with the 
retardation of the earth, it follows that at some epoch in 
the past the moon's distance was but a fraction of its 
present distance, and the lunar month was a correspond- 
ing fraction of the present month. The velocity of the 
earth's rotation was then much greater than at present, 
but not in the same ratio as the moon's orbital period was 
less. Hence the lunar month contained less than twenty- 
seven days. Tracing the relations of these motions far- 
ther and farther back, we find them approximating nearer 
and nearer to equal periods, and Mr. Darwin finds that 
this synchronism must have existed at the time when the 
moon's distance was about the sum of the two radii. He 
is led therefore to assume as the basis of a remarkable 
series of conclusions, that the moon actually did separate 
from the earth after the earth had attained the condition 
of a molten or plastic mass. The period of rotation of the 
earth at that epoch was, as he calculates, between two and 
four hours, and he assumes it at three hours. The epoch 
was not less than fifty-two million years ago — probably 
much more. That the earth's rotational period could not 
have been less than about three hours is manifest from 
the fact that a higher rate of rotation would have caused 
it, in the condition then existing, to fly into pieces, and 
the parts to separate from each other. 

This is the juncture at which he supposes the moon to 
have originated from the plastic mass. But why did the 
terrestial mass separate into two parts so unequal, instead 
of many parts ? The influence of solar tidal action must 
furnish the explanation. The sun was already in existence 



260 A COOLI>s"G PLAXET. 

before the moon, and a solar tide rolled around the nascent 
earth before it ever felt the lunar tide. The solar tide was 
comparatively diminutive, but it was real. The day being 
three hours long, each meridian experienced a solar tidal 
swell every ninety minutes. There existed at every point 
affected by this tide a vertical oscillation having a period 
of ninety minutes. But this is the period of natural oscil- 
lation or swing of the earth-mass. Every mass has a cer- 
tain period within which an oscillation or swing would 
naturally be accomplished, and its successive oscillations, 
like those of a pendulum, would be performed in equal 
times. The rate of oscillation depends on mass, viscosity 
and elasticity. A mass as large as the earth would com- 
plete its swing in a period comparatively long. Consider- 
ing it as a viscid body, calculation shows that its gravita- 
tional oscillation would be completed in about ninety 
minutes.* Now, suppose the tidal movement to coincide 
with the oscillation period; the rise and fall of the tide 
must tend to establish oscillations in the earth-mass. The 
tidal elevation would concur with the natural swing of the 
earth-mass; and, at a time w^hen the centrifugal tendency 
was nearly equal to gTavity, the concurrence of the tidal 
and oscillatory movements might quite overcome gravita- 
tion, and the tidally elevated mass might completely 
separate from the earth. As only the tidally elevated 
portion of the earth would be subjected to this joint 
influence, only this portion would separate, and the earth 
would not fly to pieces. f The rotary velocity which would 

* Rev. O. Fisher says four or five hours. Nature, xxv, 243. 

1 1 suspect a fallacy in this mode of reasoning. It might be correct if the 
solar tidal force could he conceived as applied successively upon the same side 
of the earth with intermissions every ninety minutes. An oscillation is a motion 
of matter in a definite direction. It must persist until a natural period is com- 
pleted. The solar tide, when the sun"s declination was zero, produced motions 
immediately successive in every direction around the circumference of the equa- 
torial zone. How could such motions generate a vibration of the earth? An in- 
cipient vibration generated by the tidal influence in a certain direction at one 



TIDAL ACTION 11^ PLANETARY HISTORY. 261 

disrupt the earth as a whole into many pieces did not quite 
exist. 

That two moons did not originate from the tide and 
anti-tide may be explained by the inferior elevation of the 
anti tide. It might be further explained on the principles 
just set forth if it could be shown that the period of the 
earth-oscillation was three hours instead of ninety minutes. 

Such, according to Darwin's theory, must be regarded 
as the jDrobable beginning of the lunar-terrestrial history. 
We might speculate as to the antecedents of this rapid 
rotation. The earth in cooling and shrinking from a 
nebulous state must, on the principle of equal areas, have 
undergone great rotary acceleration. This would be true 
whether the moon was disengaged as a nebular annulus, 
or later by a tidal disruption, as just explained. But we 
are not in possession of data enabling us to determine cer- 
tainly which possible origin of the moon has been realized. 
There are, however, so many analogies, and so many phys- 
ical considerations pointing to the origin of planetary and 
lunar masses through a stage of annulation, that there 
seem to be good grounds for doubting whether Mr. Dar- 
win's primitive, though plausible, assumption represents 
an actual chapter in the evolution of the lunar-terrestrial 
mass. The doubt is strengthened by the impossibility of 
establishing a similar inference in the case of other planets. 

Some special considerations, however, bear upon the 
question. The disengagement of a satellite, whether 

moment, would be destroyed the next moment, by a change in the direction of 
the pull, and the inauguration of a new vibration in the changed direction. It 
would seem that the oscillative capacity of the earth must be nugatory at the 
crisis of a Innar birth. Nor does this adjunct appear necessary. If the moon 
originated as supposed, the solar tide alone was sufficient to determine the isola- 
tion of a mass. The centrifugal tendency continuing to increase, the time would 
arrive when gravitation would be overbalanced. It would of course be the most 
protuberant part of the equatorial belt which would first reach and pass the limit 
of equilibrium. That is, the mass uplifted in a solar tide must necessarily be the 
mass detached, regardless of any measure of oscillation in the earth. 



262 A COOLIXG PLAXET. 

through annulation or disruption, takes place when the 
rotational velocity of the planet has attained that crisis in 
which the equatorial centrifugal tendency equilibrates the 
gravitational. As the result of contraction, the rotational 
velocity increases, and the equilibrating rate is continually 
approximated. But meantime, two other actions are in 
progress, one of which opposes and the other limits the 
occurrence of a secondary birth. Solar tides alwaj^s exist, 
and they always neutralize to some extent the tendency to 
accelerated rotation. And further, the process of cooling 
and condensation ultimately reduces the planet to a condi- 
tion of fluidity, viscosity or solidity, in which the rate of 
rotation required for the disengagement of a satellite is so 
high that the formation of a satellite is no longer probable. 
Now, in planets near the sun, where the solar tidal action 
is great, we may easily conceive that the retarding action 
has been so strong that the requisite rotational velocity 
for the disengagement of a satellite was never attained. 
Accordingly, Mercury and Venus are without satellites. 
On the other hand, in the remote situations, where the 
solar tidal action is feeble, the rotary acceleration may 
have been so little impeded that two or more lunar births 
may have occurred before the planet passed the annulating 
phase of matter. This is the more likely from the superior 
energy of rotation possessed by larger masses. Accord- 
ingly, from Mars to Neptune, we observe planets attended 
by several moons. Between these two regions, that is, in 
the zone occupied by the earth, the influence of the solar 
tide may have been such as to delay the crisis until the 
planet had reached the molten or viscous stage. It is not 
impossible, therefore, that the circumstances of the disen- 
gagement of our moon were different from those existing 
in the case of other moons. It may be that our moon was 
thrown off from the semi-fluid terrestrial sphere, while the 
other moons of our system passed through the annular 



TIDAL ACTIOK IX PLAXETAIIY HISTORY. 263 

stage. There are some good grounds, at least, as Mr. G. 
H. Darwin has sliovvn, for supposing our inoon originated 
as described. It is a curious fact, as the same mathemati- 
cian has shown, that similar reasoning does not show that 
the satellites of Mars, Jupiter and Saturn originated in a 
similar way.* 

However the question of the annular origin of our 
moon may be decided, we have adequate reason for believ- 
ing that the earth and moon were formerly in such rela- 
tions that the lunar tidal effect was very much greater than 
at present. On the Darwinian premises, Professor Robert 
S. Ball,! of Dublin, has lately advanced the opinion that 
enormous lunar tides were produced upon the earth dur- 
ing the Palc^ozoic ages. He thinks it not unreasonable 
to suppose that during Palaeozoic time the moon's dis- 
tance was not over one-sixth of its present distance from 
the earth. As the moon's tide-producing effect is in- 
versely as the cube of the distance, at one-sixth of the 
present distance the effect must have been 216 times as 
great as at present. If, therefore, the modern oceanic 
lunar tide is assumed as three feet, the oceanic tide with 
the moon only 40,000 miles distant, must have risen 648 
feet.t Such a conception is startling. Such a rise and 
fall of the ocean-level along a continental shore would 
pour over the land twice a day a volume of water whose 
power and destructiveness it is impossible to picture. 
Such a rise in the Atlantic Ocean would send a flood up 

*G. H. Darwin, Proc. Roy. Soc, Jan. 20, 1881. 

t In a lecture delivered before the "Midland Institute," Birmingham, Eng- 
land, October 24, 1881, and published in A^w^wre, xxv, 79-82, 103-7, Nov. 24 and 
Dec. 1, 1881. Prof. Ball is Andrews Professor of Astronomy in the University 
of Dublin, and Royal Astronomer of Ireland. 

t The linear height of the tide, however, is not quite proportional to the 
tidal force. It might be added that with the moon at such a distance, the terres- 
trial day would have been about seven hours. This increased frequency would 
increase the effects of denudation in three ways: (1) By the greater volume of 
the water acting; (2) by the greater frequency of its action; (3) by the greater 
velocity of its motion during the rise and fall of the tide. 



264 A COOLING PLAXET. 

the St. Lawrence River to Niagara Falls — into Lake Erie 
and all the way round to Chicago. It would convert all 
New England into an archipelago. All the cities of our 
eastern slope would be inundated. The great "bore" 
would roll up the Mississippi nearly to St. Paul. St. 
Louis, Memphis, Vicksburg and New Orleans would be 
submerged. The greater part of all the Gulf states 
would, for a few hours, be sea-bottom. Then the level of 
the ocean would rapidly subside. The waters would be 
poured back from the continent with the powers of a 
mighty flood. All the channel-ways would be rapidly 
deepened, and enormous volumes of sediment would be 
carried out to sea. Then the tide would surge back and 
the vast scouring process would be repeated. Well might 
the originator of the conception claim that if astronomy 
could ever prove the existence of such tides during Pa- 
laeozoic time, some of the views of geologists would be 
"absolutely demolished." Sir Charles Lyell argued that 
the events of Palaeozoic time were produced by such 
agencies as w^e now behold in action. Enormous sedimen- 
tation took place, but modern geologic forces are ade- 
quate, he thought, for its accomplishment, if we give 
them unlimited time. But physical science, as we shall 
see, does not allow the geologist unlimited time. He 
must shape his theories to a certain measure of time. 
Now here, exclaims Professor Ball, is the key to the whole 
matter. The 40,000-mile moon set the tide to work with 
two hundred-fold energy, as compared with modern tides, 
and all the sedimentation was accomplished easily within 
the time allotted by astronomy. 

But now the geologist reexamines the data which 
belong to his province of investigation. If, during Palae- 
ozoic time such terrestrial tides tore through the land, 
some records of their tremendous destructiveness must be 
preserved. Do we find them ? Do we find the Palaeozoic 



TIDAL ACTIOJ^ I:N' PLA^-ETARY HISTORY. 265 

strata composed of such enormously coarse materials as 
must have been spread over portions of the ocean's bot- 
tom by the hypothetical high tides? Do we find the sedi- 
ments disposed in that state of confusion which must 
have resulted from such violent movements of the waters? 
We are compelled to reply in the negative. This may 
almost cause a feeling of regret, since Prof. Ball's theory 
is so ingenious, so beautiful and so apt. But the truth, 
when we find it, will be equally beautiful and equally apt. 
The Paljpozoic sediments have been deposited, for the 
chief part, in quiet seas. The deep beds of limestones 
and shales are spread out in sheets continent wide, which 
testify unmistakably to placid waters and slow deposition. 
Even the sandstones and grits give no evidence of such 
tremendous agitations of sea and sediments as 600-feet 
tides would imply. If such tides ever existed, it was 
anterior to the Palaeozoic ages.* 

But if Professor Ball has erred in locating such tides 
in Pah^ozoic time, it may only be an error of location. 
Before Palaeozoic time were other vast aeons of duration, 
and vast processes of sedimentation, of which we have 
but a dreamy and ill-defined conception. Here, certainly, 
was scope enough of time and space for 600-feet tides to 
carry on their work. Do the Eozoic strata afford any 
stronger evidence of so rapid and violent accumulation 
as such tides would imply? The response which they 
render to this inquiry must still be regarded as negative. 
Their condition, however, seems to carry us back to an 

* Such views have been published by Professor J. S. Newberry. See Trans. 
N. Y. Acad. Sci., Jan., 1882; Nature, xxv, 337, Feb. 10, 1882, and xxvi, 56, May 
18, 1882. Mr. Darwin himself dissents from Professor Ball's application of his 
theory, in Nature, xxv, 213-4. Compare, also, on this subject, C. Callaway, 
Nature, xxv, ,385; A. Hale, ibid.; J. Y. Elsden, Nature, xxv, 409; Haiighton, 
Froc. Amer. Assoc, Montreal, Aug. 28. 1882. Professor Ball replies to his critics 
in Nature, xxvii, 201-3, Dec. 28, 1882. Mr. J. G. Grenfel also argues that high 
tides would deposit fine sediments (Nature, xxvii, 222), but he overlooks the in- 
land action of a rushing tidal flood. 



266 A COOLIK-G PLAXET. 

age when greater violence prevailed than characterized 
the subsequent Palfeozoic time. It is easy to suppose that 
the manifest tumult of Eozoic time was only the subsi- 
dence of a greater tumult in a still earlier age. Certainly, 
it must be admitted that most of the materials of the 
Eozoic rocks are coarser, and seem to have been more 
rapidly accumulated than those of any later system. Here 
are conglomerates containing rounded, flinty constituent 
masses, sometimes of huge dimensions. And the enor- 
mous thickness of these primitive strata exceeds by far 
any thickness known among later sediments. At the 
same time we find vast masses of crystalline limestone 
interstratified among the oldest rocks known ; and we are 
accustomed to refer such sediments to periods of compara- 
tive quiet. It is doubtful if even in the deep sea compara- 
tive quiet could be said to reign where the surface rises 
and sinks 600 feet every eight hours. Manifestly, any 
high tides of Eozoic time would not have been intermitted 
for the deposition of calcareous materials, to be after- 
ward reestablished. On the whole, the general aspect of 
the lithological masses of Eozoic time is such as might 
most reasonably be ascribed to agencies like those opera- 
tive in sedimentation in modern times. We must admit, 
however, that they were generally more energetic, though 
at intervals their violence subsided to a state of limestone- 
making repose. The necessary characteristics of extraor- 
dinary tidal action are not distinctly manifest in the oldest 
strata that have been exposed to our investigation. 

But it is not necessar}^, even yet, to renounce the con- 
ception of primitive high tides. There is no evidence 
whatever that the oldest strata ever exposed to human 
study ars the oldest that ever existed. The conglomer- 
ates even of the Laurentian are but the ruins of some 
older sedimentary rocks. To what greater depth sedi- 
mentary strata extend we can only conjecture. Perhaps 



TIDAL ACTTOK 1^ PLANETARY HISTORY. 267 

they reach down to the zone of temperature where all 
rocks are at a molten heat, and perhaps in a molten condi- 
tion. It may be that in these deeper and older beds would 
be discovered the evidences of accumulation under the 
agency of tides enormously high. It is even conceivable, 
if not probable, as we shall hereafter see, that a large por- 
tion of the oldest sediments ever deposited has been re- 
duced again to a state of fusion, and that in these wasted 
primitive beds were impressed the evidences of high tidal 
action. 

But whatever the rocks may testify, or may be con- 
ceived capable of testifying, the fact of the slow recession 
of the moon leads necessarily to the inference that the 
astronomical condition of enormous tides must have ex- 
isted at some time in the past. If the ocean was then 
in existence, it experienced this enormous tidal action, and 
its records were written in the sediments of the time. If 
shores existed they underwent enormous denudation. If 
shores had not yet arisen, the shallows of the universal 
ocean must have been stirred.* If this proximity of the 
moon had been greatly reduced before the ocean accumu- 
lated, then the vastly more energetic tidal action was ex 
erted upon a terrestrial globe of plastic or molten material. 
In this case we should have all the more reason to expect 
the formation of those meridional or submeridional trends 
discussed in other portions of this work. 

While, however, the evidence appears to be slight that 
such tides as Professor Ball conceives have ever existed 
during the earth's sedimentary history, we may readily 
admit that Eozoic and Palf^ozoic tides existed sufficiently 

* But there is, after all, one consideration which negatives the existence of 
enormously high tides since any process of sedimentation began. Such tides 
could have existed only when the earth had a rotation so rapid that its ellip- 
ticity of figure Avould have been considerably greater than at present But Sir 
William Thomson has shown, as he thinks, that no great change has taken place 
in the ellipticity of the earth since solidification began. (Thomson andTait: 
Nat. Phil., § 830.) 



268 A COOLTXG PLAKET. 

high to operate with much greater energy than modern 
tides. When the moon was 48 earth-radii distant instead 
of 60, as at present, the length of the day, according to 
Darwin's method of computation, must have been about 
16 hours; and the tide-producing power must have been 
twice its present power. But the erosive energy of the 
tide is as the square of its height, or inversely as the sixth 
power of the moon's distance.* The energy of tidal 
action would therefore be doubled by a diminution of the 
moon's distance by only one-fifth. This is a diminution 
which may be conceived to have existed within that time 
which on other grounds we are at liberty to ascribe to the 
remoteness of the Eozoic and Pahneozoic stages of terres- 
trial development; and the corresponding double tide is 
one which would have quadrupled the energy of tidal 
action without working any greater confusion in the order 
of the sediments than the actual condition of the strata 
seems to imply. This consideration enables us to reduce 
Eozoic and Paleozoic time to one-fourth the duration 
indicated by the present rate of tidal erosion. 

Tidal erosion, however, is certainly not the principal 
agency in the disintegration of rocks and the formation of 
materials for sedimentary processes, though the contrary 
view was held by the older geologists, and is still held b}' 
some.f Atmospheric and fluviatile denudation, extend- 

* If c? and d' be two different distances of the moon, and h and h', the corre- 
sponding heights of the tides, and E and E' the corresponding rates of retarda- - 
tion of the earth's rotation, then, supposing the linear height of the tide to be 
in the simple ratio of the moon's tidal etliciency, 

h : h' :: d'^ : d^, and h^ : A'2 :: rf'C : d^. 
If the two distances are 60 and 48 earth-radii, 

h : k' :: (48)'' : (60)3 ^ (4)3 . (5)3^ 1 : 2 nearly. 
Also, E : E' :: K^ : /t'2 =rf'8 : rf«. 

But the erosive power of the oceanic tide results from the same friction which 
acts as a retarding agency, and hence the efficiency of tidal erosion is as the 
square of the height of the tide, or inversely as the sixth power of the distance 
of the tide -producing body. 

t Von Richthofen: China. Vol. ii. 



TIDAL ACTI0:N' 1^ PLAIS^ETARY HISTORY. 369 

ing over the entire surfaces of continents, plays perhaps, a 
more important part than has generally been conceived. 
I shall cite hereafter, some recent views concerning the 
rate of denudation of various hydrographic basins. In 
this connection I desire only to state that atmospheric, flu- 
viatile and torrential actions must have been materially 
augmented at the time when the moon's distance was 48 
earth-radii, and the day was 16 hours long. It is manifest, 
as Mr. G. H. Darwin has reminded us, that "on similar 
planets at equal distances from the sun, and with the same 
depth of atmosphere, the linear velocity of the wind should 
vary as the linear velocity of a point on the planet's 
equator." At the time when a terrestrial rotation occu- 
pied but 16 hours, the trades and anti-trades must have 
travelled with a velocity fifty per cent greater than at pres- 
ent. We can readily conceive the probability that atmos- 
pheric movements so much more rapid must have aug- 
mented correspondingly the efficiency of wave-action and 
the disintegrating- power of the rains, and at the same 
time have greatly increased the volume of precipitation 
and tlie frequency of storms. Such aggravated intensity 
of meteorological forces must have been coincident with 
the superior energy of tidal erosion. Both causes in con- 
currence must, beyond question, have expedited materi- 
ally the geological work whose records are preserved in 
our oldest strata. 

The subject of high primitive lunar tides has been here 
considered in more especial relation to the lunar-terrestrial 
system, because the data and the evidences of such action 
would be more accessible in this case. But the question 
is one of general and cosmic significance, and occasion 
will again arise to refer to the subject in connection with 
the present condition of the planet Mars. 



270 A COOLIKG PLAi^ET. 

§7. LIQUEFACTION OF WATER. 

Subsidence of temperature to the point where water 
should pass from the gaseous to the vaporous condition 
must constitute an epoch of the utmost significance in 
the early life of a planet. That point on the earth is 
212° Fahr. or 100° C, at the level of the sea. But it is 
well known that as the pressure diminishes, as in ascend- 
ing a mountain, the steam point is lowered, while an 
increase of pressure raises the steam point. In fact, it 
has lately been claimed by Mr. T, Carnelly that water 
may be subjected to such pressure that it not only does 
not become steam at 212°, but does not even become 
liquid.* The well established facts indicate that on a 
planet of small mass, and correspondingly low atmospheric 
pressure, aqueous condensation would not take place until 
the temperature had subsided below the terrestrial stand- 
ard; while on a planet of larger mass than the terrestrial, 
condensation would begin at a temperature above the ter- 
restrial standard. 

The temperature of the solidifying point also varies 
with the pressure. Professor James Thomson first con- 
cluded, on theoretical grounds, that when a substance ex- 
pands in passing from the solid to the liquid state, the 
temperature of liquefaction is raised by increase of pres- 
sure; and when it contracts in liquefying, as in the case of 
ice, the melting point is lowered by increase of pressure. 
This deduction was experimentally verified by his brother. 
Sir William Thomson,! who found that the melting point 

*T. Carnelly, Nature, xxii, 435, where he announces an experiment in which 
solid water (called, "ice") exists at a burning temperature. See also, Nature, 
xxiii, 264, 288, 341, 383, and especially communications by O. J. Lodge and J. B. 
Hannay, pp. 504 and 505. See finally, Ptoc. Roy. Soc, 6 Jan., 1881, cited in 
Amer. Jour. Sci., Ill, xxi, 385-90. 

+ Sir W Thomson, Phil. Mag., Ill, xxxvii, 123; Poggendoff's Annalen, Bd. 
Ixxxi, S. 163. See also. Trans. Geol. Soc, Glasgow, vi,41-2. The following is, 
perhaps, the rationale of the law: A certain amount of pressure seems to be 



LIQUEFACTION" OF WATEE. 271 

of ice is lowered 0°.059 C. for a pressure of 8.1 atmos- 
pheres, and 0°.129 C. for a pressure of 16.8 atmospheres. 
Mousson*, also, proved that ice melts at —18° to — 20° 
C, when subjected to a pressure of 13,000 atmospheres; 
but it was not shown that all this pressure was neces- 
sary. Clausius subsequently showed, from theoretical 
considerations, that the freezing- point of water must be 
lowered 0°.00733 C. for every atmosphere of increased 
pressure — a result which agrees with experiment. f Di- 
minished atmospheric pressure would therefore raise the 
freezing point of water; and we might conceive the pres- 
sure so diminished that the lowered steam point would 
coincide with the elevated ice point. Under such circum- 
stances, water would present the same relations as certain 
substances on our planet which never liquefy, but pass 
directly from the solid to the gaseous state when heat is 
applied.}; On such a planet there could be neither clouds, 

requisite to restrain the molecules of a solid, within certain limits of tempera- 
ture, from relaxing their bonds to each other; the same as a certain amount of 
pressure, within certain limits of temperature, is necessary for restraining the 
molecules of the fluid from flying apart — the pressure in all cases being external. 
If the state of looser union requires more space, increase of pressure opposes 
the change of state, and a higher degree of intermolecular repulsion is required. 
Increased heat furnishes this. If the state of looser union requires less space, 
increase of pressure helps to reduce the body into such diminished space, and 
hence less repulsive energy among the molecules is required. That is, the tem- 
perature of fusion is lowered. Why a state of looser union requires less space 
(higher density) may perhaps be explained by the existence of larger intermolec- 
ular intervals, where, as in ice and most solids, the structure is ci*ystalline — 
that is, having the molecules arranged according to a geometrical method. 

Under this law the solidification by enormous pressure of molten mineral 
substances at temperatures above their fusing points cannot be conceived as a 
crystalline solidification resulting from a certain adjustment of temperature and 
pressure, but solidification resulting from the approximation of the molecules 
under the same amorphous arrangement as characterizes the liquid. Hence the 
state of solidity from pressure implies a higher density than the fluid state, 
while solidification from cooling implies a lower density than the fluid possesses. 

*Mousson, Pogg. Annal., cv,li}l. 

+ R. Clausius : Die mechanische Wdrmetheorie, 2d ed., i, 173. If we multiply 
0°.00733 by 8.1 and 16.8 we get 0°.O59373 and 0°. 123144 — results practically iden- 
tical with Sir William Thomson's. 

t Compare Clausius: Wcirmetheorie, I, Absch. vii, § 6, Uebergang aus dem 
Festen in den luftformigen Zustand. 



272 A COOLING PLACET. 

rain nor seas. Water would be born out of steam, in a 
solid snowy state, would descend like a shower of dust, 
and rest forever as rocky material. On a planet larger 
than the earth, where liquefaction from aqueous gas or 
invisible steam takes place at a higher temperature, the 
water must not only be hotter, but, under the higher pres- 
sure, must absorb a larger proportion of gaseous substances. 
From both these causes, meteoric water on such a planet 
must be a more efficient chemical agent, and must act with 
increased energy on the rocky substances of the planet. 

As to substances which expand in passing from the 
solid to the liquid state, only a few experiments have been 
made. In fact, there are very few substances of which it 
is certain that such expansion takes place. Those experi- 
mented on are spermaceti, paraffine, stearine, wax and sul- 
phur; and it has been proved that the melting point is 
universally raised by pressure.* Sir William Thomson, 
as before stated, inclines to the opinion that ordinary 
rocks belong to this class; but I think I have cited suffi- 
cient evidence that they belong to the same class as water, 
and hence have their solidifying point lowered by increase 
of pressure. 

But, returning to the inaugurative stage of planetary 
hydratation, we can easily conceive the progressive ad- 
vance of water formation on a planet. The first conden- 
sation would be revealed by the filmiest clouds in the 
highest and coolest region of the atmosphere. On a planet 
of the mass of the earth, or larger, it would seem proba- 
ble that the crust must still exist in a 'state of incan- 
descence. f Such questions are within the reach of mathe- 

* Hopkins, Report Brit. Assoc, 1854, 57; Bimsen, Fogg. Annul. , Ixxxi, 562. 

t On the earth all substances retain a red heat till the temperature falls 
below 977° Fahr. (J. W. Draper, Amer. Jour. Sci., 67, January, 1877.) It is suppos- 
able that though the crust might have attained a dark temperature, the forma- 
tion of a blanket of clouds would so arrest radiation that a glowing heat might 
be again imparted to the crust. 



LIQUEFACTION^ OF WATER. 273 

matics. On a small planet condensation would not begin 
until the surface bad passed the stage of incandescence. 

The accumulation of aqueous vapor in the higher re- 
gions would continue until the cloudy mass had settled 
through increasing density, to lower regions. Each stage 
of encroachment on the lower strata of the atmosphere 
must cost the clouds volumes of vapor dissipated into gas. 
Meantime the light of the sun becomes completely ex- 
cluded, and the planet must be ^^alled in impenetrable 
darkness, unless the ignited crust send its lurid gleam to 
redden the black vault of curling and threatening vapors. 
Eventually the condensation must reach such a point that 
the heat of the atmosphere can no longer prevent the rains 
from descending. Ages may elapse before a drop can 
penetrate to the planet. Ocean volumes may be dissi- 
pated into steam in mid air ; but larger oceans must 
return to the conflict with the heat. Meantime the equi- 
librium of the electrical forces is disturbed, and sheets of 
lightning glimmer through the stormy air, and thunders 
ever renewed must jar the fabric of a world, and shake its 
watery pall to ever-augmented precipitation. 

The forces of heat in the progress of such a storm, 
must undergo increasing wastage. Radiation is more vig- 
orous, now that the cool sheet of clouds has marshalled its 
attacking rains in closer proximity. Convection steals 
away immense volumes of heat, as the stream of new-made 
vapors rises perpetually to the cooler regions. The crust 
at length glows with a dimmed ruddiness, and then the 
last ray of the planet's solar character expires. The secu- 
lar storm, with a terrific grapple of the elemental forces, 
settles dowii on the seething surface, and holds possession 
with the grim violence of lightnings and floods. In this 
last struggle the ocean is born, and begins to stretch its 
liquid arms around the world. It is a boiling, bubbling, 
ocean. It saturates the atmosphere with columns of pale 
18 



374 A cooli^^Ct pla^^et. 

steam. It is an ocean of acid waters. Not content to 
vanquish the powers of fire in their very intrenchments, 
they begin to disintegrate and destro}- the rocky substance 
of the intrenchments themselves. A new war springs into 
existence. The chemical affinities turn their hands against 
each other, and rapes and robberies and reprisals make 
the subaqueous history of a planetary age.* Out of these 
reactions come the salts which the sea holds in solution. 
Out of these reactions come the earliest precipitations on 
the ocean's floor. 

The continued progress of cooling effects, sooner or 
later, the transfer of the body of water from the atmos- 
phere to the planetary surface. Through the thinned 
clouds gleams the sunrise of another £eon. At length 
the exhaustion of the clouds reveals again the ancient sun, 
and the purified sky, and the action of the planetary 
drama now proceeds in the silent depths of the waters. 

§ 8. TRANSFORMATIONS OF THE PLANETARY CRUST. 

There must be a fire-formed crust on every planet. 
The floor on which the first ocean rests can have no other 
than an igneous origin. To tell me that no geologist has 
ever seen the earth's primeval crust does not shake my 
conviction that thus "the solid earth began." There are 
good reasons for not entertaining the expectation of ever 
'ooking upon any exposure of the original fire-formed 
crust. It no longer exists. Nor indeed, can we believe that 
even the oldest ocean-formed rock-strata loh our planet have 
been preserved from destruction. At the commencement 
of sedimentation on any planet, the crust has attained 
such thickness that a temporary equilibrium exists be- 

* These chemical reactions in the primeval history of the earth have been 
especially studied by Dr. T. S. Hunt. See his Chemical and Geological Essays. 
See also, an outline of these reactions in the present writer's Sketches of Crea- 
tion., ch. vi. 



TRAJS'SFORMATIOKS OF THE PLAITETARY CRUST. 275 

tweeii the thermal action within and the refrigerative 
action without. The crust presents such a protection to 
the included heat that no further thickening is demanded, 
except as the mass of the planet cools. A thinner crust 
would expose the internal heat to more rapid radiation, 
and new layers of crust would be added to the under side. 
A thicker crust would give the included thermal forces 
the ascendency, and some layers would be melted from 
the under side until the facility of thermal conduction and 
radiation should be sufficient to exhaust the surplus energy 
of the heat within. 

Now if, while such a crust exists as equilibrates the 
action of internal and external forces, a sheet of oceanic 
waters overspreads the surface; still more, if layers of 
marine sediments become accumulated, the crust will ex- 
perience such a thickening that the forces of heat will 
preponderate, and by fusing some of the under layers 
reduce the crust to the equilibrating thickness. The con- 
tinued accumulation of sedimentary deposits will be ac- 
companied by the continued encroachment of a fusing heat 
upon the under side of the crust.* It is plain that the 
continuance of these processes is liable not only to remove 
and re-fuse totally the whole thickness of the fire-formed 
crust, but also, any assignable thickness of the sedimentary 
or super-crust. This process may continue during the 
whole of the planet's refrigerating history, though at no 
time can the encroachment at the bottom quite equal the 
sedimentary additions at the surface; since because the 
planet is necessarily cooling as a mass, its crust must ex- 
perience a net increase of thickness. The final result 

* This idea seems to have been first shadowed forth almost simultaneously 
by Professor Charles Babbage and Sir John Herschel, in 1836, 1837 and 1838 (see 
Ninth Bridgewater Treatise, App. G; also London and Edinb. Phil. Mag., v. 
213). Sir John's suggestions are embodied in the Ninth Bridgewater Treatise, 
App. I, in three letters, dated Feb. and Nov., 1836, and June, 1837. See also 
Leouhard's Jahrbuch, 1838, 98; 1839, 347. 



276 " A COOLIXG PLAXET. 

might be that sedimentary beds, accumulated even after 
the dawn of the organic epoch, might come to occupy the 
lowest position. Organic forms comparatively high might 
seem to begin the succession of life by holding position in 




Fig, 47.— Ascent of Isothermal Planes ix a Planet's Crust. 

the oldest accessible rocks. Thus the palicontological in- 
vestigator would be foiled by an illusion. 

These changes are illustrated by the accompanying dia- 
gram. Figure 47. The line c c' represents the bottom of 



TRANSFORMATIONS OF THE PLANETARY CRUST. 277 

the sea, on which sediments are in process of accumulation. 
Under some circumstances the ocean basin would thus 
undergo a process of filling, and the sea-bottom c c' would 
occupy successively higher positions. This would be the 
case if the general configuration of the planetary crust 
were to remain unchanged, the material deposited in the 
sea being only the amount removed from the land. In 
most cases, however, slow wrinkling would be in progress, 
so that the ocean's bottom would suffer a gradual subsid- 
ence. Let us assume that the bottom c c' remains at a 
constant level notwithstanding sedimentary accumulation, 
the sinking being equal to the amount of sedimentation. 
Then let c r or c' r' represent the constant thickness of 
crust determined by the thermal conductivity of the crust- 
materials. A, on the left, represents a section of the fire- 
formed crust, and M, a portion of the underlying molten 
matter. 

NoWj if marine sedimentation accumulates the layer B, 
the ocean bottom retaining its level, a portion of A repre- 
sented by A', will be sunken into the molten mass M, and 
reduced to a state of fusion. If another sedimentary layer 
C, is laid down, nearly the whole of A may be sunken and 
merged into the fused mass M; and the heat conducted 
into B will partially obliterate its stratification by crystalli- 
zation and other modes of metamorphism. If, thirdly, we 
suppose the layer D to be deposited and sunken, the whole 
of A may now become merged in the molten mass, and a 
portion of B represented by B' Avill suffer the same fate. 
The remainder of B will become highly metamorphosed, 
and similar action will extend upward into C Evidently, 
the same process may continue until some fossiliferous for- 
mation becomes sunken to the line r r' . 

The line r r marks the isothermal plane at which the 
temperature is at the fusing point of the rocks. Planes of 
lower temperature pass through the planetary crust in 



278 A COOLING PLANET. 

positions above this and approximateh' parallel with it. 
The mass M, below, as before stated, may be assumed as 
nearly uniform in temperature to the planetary centre. 
The progress of sedimentation thus appears to cause a rel- 
ative ascent of the isothermal planes through successively 
newer formations in the planetary crust. 

§ 9. PLANETOGRAPHIC EFFECTS OF CERTAIN CHANGED 
ASTRONOMICAL CONDITIONS. 

1. Changes in Yelocity of Jiotation. — It has been 
shown that one of the actions of tides upon a planetary 
body tends to diminish its rate of rotation. Correspond- 
ingly, its equatorial protuberance wdll tend to diminish. 
In the case of a planet still retaining its liquid condition, 
the equatorial subsidence will keep nearly even pace with 
the retardation. To whatever extent viscosity exists, the 
subsidence will follow the retardation. There will exist 
an excess of protuberance be3^ond the equilibrium figure 
due to the actual rotation, and this will act as an additional 
retardative cause. In the case of an incrusted and some- 
what rigid planet, the excess of ellipticity would attain its 
greatest value. It would continue to augment until the 
strain upon the mass should become sufficient to lower the 
excessive protuberance to the equilibrium figure. The 
recovery of this figure might take place convulsively. The 
equatorial regions would then subside and the polar would 
rise. In the case of an incrusted planet extensively cov- 
ered, like the earth, by a film of water, retarded rotation 
would be attended by a prompt subsidence of the equa- 
torial waters, and rise of the polar waters to about twice 
the same extent. In other words, the equatorial lands 
would emerge and the polar lands would become sub- 
merged. The amount of emergence would diminish with 
increase of distance from the equator, and the amount of 
submergence would diminish with increase of distance 



EFFECTS OF ASTRONOMICAL CHAN"CtES. 279 

from the pole. In about the latitude of 30° the two ten- 
dencies would meet and neutralize each other. Under 
these conditions, an incrusted and ocean-covered planet, 
since it must be undergoing a process of rotary retarda- 
tion, must possess the deepest oceans about the poles, and 
the shallowest about the equator. The first emergences 
of land, accordingly, will take place within the equatorial 
zone; and the highest elevations and greatest land-areas 
will exist within that zone. The elevation of equatorial 
land masses would interpose new obstructions to the equa- 
torial ocean current. This would divert it in new direc- 
tions, and thus modify all climates within reach of oceanic 
influences. Changes of currents would necessitate the 
migration of marine faunas, and changes of climate would 
modify the faunas and floras of the land. 

But the protrusion of the equatorial land-mass could 
not increase indefinitely. The same central force which 
retains the ocean continually at the equilibrium figure, 
strains the solid mass in the same direction. The strain 
must at length become greater than the rigidity of the mass 
can withstand. The equatorial land protuberance will 
subside toward the level of the ocean. Some parts of the 
ocean's bottom must correspondingly rise. Naturally, the 
parts about the poles will rise most. Thus some equatorial 
lands will become submerged and some northern and 
southern areas may become newly emergent. 

But these vertical movements would not be arrested 
precisely at the point of recovery of the equilibrium 
figure. As suggested by Professor J. E. Todd*, and less 
explicitly by Sir William Thomson, the movement would 
pass the equilibrium figure to an extent proportional to 
the cumulation of strain. The equatorial region would 
become too much depressed and the polar regions too 
much elevated. The effect of this would be to accele- 

* Todd: Ame7\ naturalist, xviii, 15-26. 



280 A COOLING PLAIs^ET. 

rate the rotation sufficiently to neutralize the ceaseless 
tidal retardation. The day would be shortened. The 
ocean would rise still higher along the shores of equa- 
torial lands, and subside along the shores of polar lands. 
An extension of polar lands would immediately modify 
the climates of the higher latitudes. They would become 
subject to greater extremes. A considerable elevation of 
polar lands would diminish the mean temperature, and the 
region of perpetual snow would be enlarged. These effects 
would visit the northern and southern hemispheres simul- 
taneously. 

Such effects would follow from an excessive subsidence 
of equatorial lands. But the constant retardative action 
of the tides would cause the equatorial lands again to 
emerge, and protrude beyond the limits of the equilibrium 
figure attained in a later age. Thus the former conditions 
would return, and the former events would be repeated. 
In the nature of force and matter, these oscillations should 
be repeated many times. Professor Todd suggests that 
the present terrestrial age is one of equatorial land sub- 
sidence, and of high latitude emergence. Immediately 
preceding the present, the Champlain epoch was one of 
northern and probably of south polar subsidence; while 
further back, in the Glacial epoch, we have evidence of 
northern and perhaps also of south latitude elevation. He 
thinks the series of oscillations may be traced backward 
to the epoch of the earliest solid records of the earth's 
changes. 

The periodical elevation and subsidence of the equa- 
torial and polar regions would change the positions of ocean 
currents, and consequently the oceanic temperatures in 
given situations would be changed. Change of depth 
alone would result in change of temperature, since recent 
researches have shown that the abysses of our oceans are 
filled with water possessing a polar temperature, while 



EFFECTS OF ASTRONOMICAL CHANGES. 281 

shallower seas possess temperatures graduated to their 
depth, and influenced near tlie surface by the latitude. 
Changes of oceanic temperature, produced by either of 
these causes, would lead to the extinction or migration of 
faunas. As the movements here contemplated are cyclical, 
the same conditions would recur again and again; and 
accordingly tlie same fauna might return again and again 
to the same region, with intervals of occupation by another 
fauna. Progressive sedimentation would preserve the 
records of such faunal alternations; and there would be 
presented the phenomena of " colonies," " reapparitions," 
and other faunal dislocations in the vertical and horizontal 
distribution of fossil remains. These phenomena are 
well known to the student of geology.* The progressive 
regional differentiation of lands and seas due to the secular 
loss of planetary heat would be a cumulative cause of slow 
but inevitable changes in the fauna at its successive recur- 
rences, and would limit the number of recurrences of the 
same fauna. This action would be most sensibly felt in 
shallower seas and on land. The depths of the ocean, 
which retain most uniformly their cosmic conditions, would 
witness the longest series of recurrences of the same or a 
kindred fauna. 

2. Retarded Orhital Motion. — Strong deductive indi- 
cations exist, as has been shown, that the orbits of the 
planets and satellites have been enlarged. Not to speak 
of other causes, this is one of the indirect effects of tidal 



* M. Joachim Barrande, Colonies Bull. Soc. geol. de France, xvii, 602, 1860; 
Defense cles Colonies, Part I, 1861; Part II, 1862; Part III, 1865; Part IV, 1870; 
Part V, 1881. Prof. James Hall, Trans. Amer. Phil. Soc, 1866, p, 246, in advance of 
Pakeontology of Neto York, vol. iv, — these views being repeated at meeting of 
National Academy, Hartford, 1867, and indorsed by Prof, L. Agassiz; A. H. 
Worthen, Proc. A. A. A. S., xix, 172-5, 1870, Troy ; but see Prof. Hall's criticisms, 
id., xxii, 321-35, reprinted in Appendix to Twenty-seventh Rep. New York Regents, 
117-31 ; Prof. H. S. Williams, On a Remarkable Fauna at the Base of the Chemung 
Group in, New York, Afner. Jour. ScL, III, xxv, 97-104, Feb., 1883, and Note, p. 
311; but see S. Calvin, Amer. Jour. Sci., Ill, 432-6. 



282 A COOLIXG PLAXET. 

action. Each planetary year has, in the remote past, been 
shorter than at present. In the same proportion, each 
season on each of the planets — if we may generalize the 
term season in a qualified sense — has been shorter. It 
ought not to be supposed that the epoch of sensibly shorter 
years has been so recent as to offer an explanation of the 
extreme longevity attributed to the " antediluyians." The 
shorter years, however, must have been experienced during 
the progress of the geological periods. Whatever actions 
accompany the transitions from summer to winter, and 
from winter to summer, must consequently have been more 
frequently repeated. All geological effects attributable to 
such actions must correspondingly have been augmented. 
Each round of the seasons brings its appropriate precipi- 
tations, erosions and disintegrations; and when these 
rounds were twice as frequent, geological changes were 
more rapid. Geological actions were also more energetic, 
in consequence of the rapidity of the transition from one 
climatic state to another. At the same time, also, the 
nearer proximity of the sun would bring a greater amount 
of solar heat, which is the prime mover in all the seasonal 
changes. Shorter years and shorter seasons imply different 
adaptations in the natures of animals and plants. The 
processes of seasonal reproduction were accelerated; and 
where the same work w^as done in less time, the functional 
powers must have moved with greater efficiency or greater 
celerity. 

3. Increase of Ohliquity of Axis to Plane of Orbit. — 
Another influence of tidal action inclines the planetary 
axis, within certain limits, at an increasing angle with the 
axis of the orbit. The most obvious consequence of this 
(which is augmented and diminished by changes in the 
plane of the orbit as compared with an invariable plane) 
is to widen the torrid and the frigid zones, and narrow the 
temperate zones. 



EFFECTS OF ASTRONOMICAL CHANGES. 283 

In the subjoined diagram, NS represents the axis in 
one state of inclination. The date is the summer solstice 
of the northern hemisphere. R R are parallel solar rays 
whose points of tang-ency with the planet's surface, as at 
P, determine the position of the polar circles, and the 
limits N P of the polar zone; C, the central ray at this date, 
vertical at T, determines the position of the northern 
tropic, T T, and the breadth, T A, of the torrid zone, and 
T P, of the temperate zone. 

Now suppose the inclination to be increased so that 




Fig. 48.— Climatic Effect of Increased Obliquity of a Planetary Axis. 

N' S' represents the position of the axis. Then N' P' will 
represent the limits of the polar zone, T A* the width of 
the torrid zone, and P' T, the width of the temperate zone. 
With an inclination of 45°, the temperate zone, in the 
sense here explained, would vanish. 

The widening of the torrid zone would extend the 
range of products depending on a torrid summer climate, 
but would depress the winter temperature along the bor- 
ders of the zone, since in winter the days would be shorter 
and the meridian sun would have less altitude. In other 



284 A. COOLIKG PLA>fET. 

words, the torrid summer would extend into higher lati- 
tudes ; but the same latitudes would experience during 
winter a lower depression of temperature than they would 
with a less axial inclination. There would be a wider 
thermal contrast between the tropical summer and the 
tropical winter throughout the whole breadth of the zone. 
This circumstance would react upon the organic kingdoms. 
Plants and animals must endure greater extremes. Those 
most susceptible to climatic influences might become 
dwarfed or exterminated. 

The widening of the frigid zone implies more sunshine 
in summer. The sun will attain to a higher elevation at 
every parallel, and the area enjoying summer days without 
a sunset will be enlarged. The consequence of this must 
be a more extensive disappearance of snow and ice, accu- 
mulated on planets with snow-capped poles during the 
previous winter. On the contrary, the increased inclina- 
tion extends the area deprived of the sun in winter, but it 
does not increase the severity of the cold ; since when the 
sun is a great distance below the horizon his influence is 
no less felt than when but a short distance below. The 
winter season would therefore not tend materially to aug- 
ment snowy accumulations beyond the amount resulting 
from a low axial inclination. The combined result of 
summer and winter would be, in this view, a diminished 
amount of snow and ice. Correspondingly, a diminished 
inclination of the axis would result in an increased amount 
of snow and ice, though the area covered would be less. 
These consequences would be simultaneous in the two 
polar zones. 

With no inclination the sun would be perpetually in 
the horizon of either pole. A temperature nearly that of 
external space would prevail uninterruptedly. But at no 
great distance from the pole, perpetual sunshine, though 
from a slanting sun, would tend greatly to the dissolution 



EFFECTS OF ASTRONOMICAL CHANGES. 285 

of snowy accumulations. At 26° from the pole the alti- 
tude of the sun would be about the same as the midday 
sun at New York at the end of December. But it would 
remain permanently at that altitude. It is doubtful 
w^hether this position of the svin would be compatible with 
a snow cap extending lower than 26° from the pole. A 
slight inclination would throw an area about the pole 
into a state of sunlessness during a portion of the winter, 
but it would gain in altitude of sun during the summer. 
On the whole, it seems very doubtful whether any inclina- 
tion, great or small, would create the conditions for a 
permanent ice cap reaching as far as the latitude of 40°.* 
4. Change in Relative Positions of Apsides and Equi- 
noxes. — The precession of the equinoxes arises from a slow 
gyratory motion of the axis of the planet, causing each 
pole to describe a somewhat regular circle. This results 
from the action of the sun upon the equatorial protuber- 
ance, joined to the resultant of the combined actions of 
the satellites, when they exist. The rate and amount of 
the disturbance is therefore connected, among other things, . 
with the amount of the protuberance and the amount of 
the inclination. The effect of this change is to cause the 
planetary axis to be inclined, at different periods, in differ- 
ent absolute directions ; and the total movement relative 
to a point in the planet's orbit is also affected by a motion 
of the apsides. In the case of all the planets except 
Venus (and possibly Neptune) the apsidal motion is 
direct, and therefore diminishes the effect of precession. 
In the case of the earth the equinoctial point falls back 
50' M annually. It would of itself, therefore, complete 
the circuit of the ecliptic in twenty-five thousand, eight 
hundred and sixty-eight years. But as the apsis goes for- 

*The reader will find some discussions of axial inclination as a cause of 
terrestrial glaciation in Drayson. <^\iar. Jour. Geol. Soc.^ xxii ; Thomas Belt, 
Id., Oct., 1874, abstract, Amer. Jour. ScL, III, ix, 313-5; Croll: Clbnate and 
Time., ch. xxv, where Drayson and Belt are discussed. 



286 A COOLIXG PLAXET. 

ward to meet it at the rate of 11", 2-4* annually, this 
would complete a revolution in one hundred and fifteen 
thousand, three hundred and two years. The approxima- 
tion of the equinox and the apsis is the sum of these 
motions, 61". 34, and hence the equinox returns to the 
same position in relation to the apse in twenty-one thou- 
sand, one hundred and twenty-eight years. The earth's 
axis was inclined exactly from the sun at perihelion, in the 
year 1248. It now (1883) consequently points 10° 49' 11" 
back (or west) of perihelion, so that perihelion is reached 
about ten days after the winter solstice. 

It results from these two secular movements that at a 
certain time, the planetary axis will lean toward the sun 
when at the aphelion point ; at another, toward the sun 
when at the perihelion point. In the former case, summer 
occurs in the northern hemisphere during aphelion, and 
winter during perihelion. In the latter case, summer 
occurs in the northern hemisphere during perihelion, and 
winter during aphelion. The terms, of course, are in- 
verted in reference to the hemisphere below the plane of 
the planet's orbit. 

In the accompanying figure, let N S represent the axis 
of a planet from such a point of view that equator, trop- 
ical and polar circles are projected in right lines. Let the 
position of the planet be perihelion, with the solar rays 
R, C, R, coming from the right. The north pole leans 
toward the sun. Summer in the northern hemisphere and 
winter in the southern, occurs during perihelion. Next, 
suppose, in the same diagram, the north pole is turned 
away from the sun at perihelion, and the solar rays 
R', C, R', come from the left. Now, icinter in the north- 
ern hemisphere and summer in the southern, occurs during 
perihelion. 

*The value? of these variations are taken from the Encyclopaedia Britan- 
nica, Art. Astronomy. 



EFFECTS OF ASTRONOMICAL CHANGES. 287 

-R 




Fig. 49. Climatic Effect of Chaxges in Relative Positions of Apsides 
AND Solstices. 



The planetary effect of such changes in the position of 
the axis during the summer and winter periods of each 
hemisphere, would be climatic. In the first case supposed, 
summer in the northern hemisphere concurs with the 
planet's greatest proximity to the sun. The solar action 
on the polar snow and ice, if they exist, would be greater 
than when summer occurs in aphelion, nearly in the ratio 
of the square of the perihelion and aphelion distances. 
In other words, the summer warmth would show greatest 
excess in planets having orbits of highest eccentricity; 
though the effect of superior eccentricity would be dimin- 
ished with increase of mean distance from the sun, and 
increased with diminution of mean distance. The concur- 
rence of the summer solstice with perihelion would there- 
fore tend to diminish polar glaciation. During the 
aphelion winter, the solar action would be diminished, 
below the solar intensity during a perihelion winter, at all 
points having the sun above the horizon; but not sensibly 
changed at points having the sun below the horizon. The 
resultant effect throughout the polar zone would probably 
be some increase of glaciation. This winter increase of 



288 A COOLIITG PLAIs^ET. 

glaciation would go far to neutralize the summer diminu- 
tion. Professor James Croll is of the opinion that in the 
case of the earth, it would entirely neutralize it; so that 
the movement of the equinox would never result in any 
change in polar glaciation.* On the contrary, MM. Ad- 
he mar f and Julien "l and jNIr. J. J. Murphy § maintain that 
the coincidence of the summer solstice with perihelion, 
and the winter solstice with aphelion would decidedly in- 
crease northern glaciation. The converse of this relation 
existed, in the case of the earth, in the year 1248, and 
these authors maintain, by means of numerous citations, 
that the winter climate of Europe was milder at that 
epoch than at present. The passage of the winter solsti- 
tial point ten or twelve degrees before the perihelion 
point already results, they say, in a perceptible increase 
of wintry cold. It is, however, scarcely credible that so 
trifling an increase of distance from the sun at the winter 
solstice should result in any perceptible change in the 
winter climate; or that the whole difference between 
perihelion and aphelion should ever cause such general 
glaciation of the northern continents as seems to have 
existed in a former geological period. This doubt may 
well be based on the summer influence of conjunction of 
summer solstice and perihelion. We are not in a posi- 
tion, therefore, to conclude that changes in the angle 
made by the line of equinoxes with the line of the apsides 
would cause any important residual effects upon planetary 
climate. 

5. Changes of Orbital Eccentricity. — The immediate 
effect of increased eccentricity is to increase the differ- 

* Croll: Climate and Time, 83; Phil. Mag., Sept., 1869. On this subject, see 
also Arago, Annuaire, 1834, and Bdinb. New Phil. Jour., vi, 1834. 

t Adhe'mar : Rtvolutions de la mer, 2d ed., 1860. 

X Julien : Couranfs et revolutions de Vatmo$.phere et de la mer. See also, Le 
Hon: L' Homme fossile en Europe, 4mc. ed., 1877, Seconde Partie. 

§ Murphy, Quar. Jour. Geol. Soc, xxv, 350. 



EFFECTS OF ASTRONOMICAL CHAITGES. 289 

ence between the perihelion and aphelion distances of the 
planet. Whatever climatic or other consequences proceed 
from this difference will be exaggerated by increased 
eccentricity. But the nature of the climatic ejffect will 
depend on the angle of the equinoctial line with the 
apsidal line, and also, whether a particular solstice occurs 
on the perihelion or the aphelion side of the equinoctial 
line. Let us suppose that the summer solstice of the 
northern hemisphere coincides with perihelion. Thus, 
with increased eccentricity, the perihelion distance in 
summer is less, and the summer, though shorter, is 
warmer; also the aphelion distance in winter is greater, 
and the winter is longer and colder. The winter will 
therefore accumulate more snow and ice, and the snow 
cap will extend to a lower latitude. But then this accu- 
mulation will be acted on by the increased summer heat. 
If, therefore, the accumulation is not sufficient to with- 
stand this increased heat, no residual effect will remain. 
If any part of the accumulation is sufficient to continue 
through the hot summer there will be a secular accumula- 
tion of northern snow and ice. But it must be mentioned 
that the solvent effect of the hot summer will not be pro- 
portional to the perihelion distance. The solar rays, fall- 
ing on surfaces of snow and ice, will be exhausted first 
in the formation of vapor, which will obstruct the access 
of solar heat, and neutralize, to a large extent, the excess 
of summer warmth. The effective solvent force of the 
solar rays may not, therefore, much exceed their force at 
the aphelion distance, and there must remain a residual 
increase of northern glaciation. This, at least, is the view 
taken by Croll. * It does not appear, however, that the 
residual increase can ever amount, upon the earth, to "a 
reign of ice," such as prevailed in the Quarternary period 

*Croll: Climate and Time. 
19 



290 A COOLIXG PLAXET. 

of geology.* Mr. Croll himself does not maintain this; 
but he argues that in the case of the earth, the configura- 
tion of the continents has been such as to direct the equi- 
noctial current, during the period of summer perihelion, 
away from the northern hemisphere, and thus indirectly to 
induce the conditions of a "reign of ice."t 

It is manifest that the production of a state of north- 
ern glaciation by the concurrence of high eccentricity and 
a perihelion summer solstice would be attended by recip- 
rocal conditions of climate in the southern hemisphere; 
and that all these conditions would be reversed by low 
eccentricity and an aphelion summer solstice. It is also 
manifest that each astronomical movement would produce 
a climatic cycle of its own — that connected with the 
eccentricity having a variable period of some tens or hun- 
dreds of thousands, and that connected with precession 
and the movement of the apsides having a period of about 
21,000 years. When the effects from the two causes 
concur, a maximum climatic effect would result; when they 
conflict, a minimum. 

* Sir J. Herschel, On the Astjonoinical Causes which may Influence Geologi- 
cal Phenomena, Geological Transactions, 1832; Treatise on A strono?ny, %S\5; 
Outlines of Astronomy, § 368; Arago, Anuuaire, 1834, p. 199; Edinb. New Phil. 
Jour., vi, April, 1834, 244; Humboldt: Cosmos,- \\\ 459, Bohn's ed ; Phys. De- 
scrip. Heaven^, 336. 

t Croll : Climate and Time ; A. Winchell : S2iai'ks from a Geologists Ham- 
mer, 175 99. See criticisms of Croll's theorj' by S. !Ne\vcomb, Amer. Jour. Sci., 
III. xi, 263; J. J. Murphy, A?ner. Jour. Geol. Soc, x.kv, 350. 1869, abstract Atner. 
Jour. Sci., Ill, xlix, 115-18; Charles Martins, Revue des Deux Mondes. 1867: W. 
J. McGee, Popular Science Monthly, xvi, 810, but with general endorsement; C. 
B. Warring: Penn. Monthly, 1880. Further on this subject the reader may con- 
sult LeHon: L' Homme fossile, pt. ii; Col. Drayson, PA?7. J/rtr/., 1871, abstracted 
in Arner. Jour. Sci., Ill, ii, 301; Sir William Thomson: Geological Climate, 
Trans Geol. Soc, Glasgow, Feb., 1877, vol. v, pt. ii; James Geikie: Prehistoric 
Europe, 1880; G. Pilar: Ueber die Ursache der Eiszeiten; Hirsch, Svr les causes 
cosmiques d(S changements de climat. Bull, de la Societe des sci., nat. de Neuf- 
chatel. Also, discussions by Croll, Heath. Moore and Pratt in the Philosophical 
Magazine, 1864, 1865, 1866; A. R. Wallace: Island Life. W. J. McGce has very 
recently vindicated the " eccentricity theory " in Amer. Jour. Sci.. Ill, xxvi. 113- 
20, Aug., 1883. 



OROGENIC FORCES. 291 

§ 10. OROGENIC FORCES. 

The inequalities in the contour of the terrestrial sur- 
face are scarcely more familiar than the orographic phe- 
nomena which diversify the visible face of the moon with 
their lights and shades. The earth and the moon are 
equally well known to be marked by mountains, valleys 
and plains. The lights and shades of the disc of Mars are 
also generally received as evidences of analogous topo- 
graphical configurations. In general, we might be led to 
believe from the study of terrestrial inequalities, and the 
terrestrial forces which seem adequate to develop moun- 
tain features, that the production of mountains is a com- 
mon incident in planetary history. We can understand, 
at least, certain modes of action which tend toward moun- 
tain development; and even if no complete and satisfac- 
tory^ theory can yet be framed, it may be gratifying to the 
reader to learn what views have been entertained, and 
what is the present state of speculation on the subject. 

In discussing the origin of mountains, and of terrestrial 
mountains in particular, it is necessary, first of all, to dis- 
criminate tnountams of elevation from mountains of 
relief. The former are eminences which have been mani- 
festly upraised above the general level of the earth's sur- 
face. The latter are saliences resulting from the erosion 
and removal of surrounding masses. The interpretation 
of erosive phenomena is something so simple that the ex- 
planation of mountains of erosion has given rise to little dis- 
cussion. In almost every case, however, a mountain mass 
inaugurated by actual elevation has been greatly modified 
by much later erosions. In many instances, indeed, ero- 
sion has completely transformed the configuration of the 
original upheaval, and it has sometimes so disguised the 
results of upheaval as to require careful study to discrimi- 
nate certainly the work which ought to be ascribed to 



292 A COOLIXG PLAXET. 

elevatory action. But in this connection we disregard en- 
tirely the sculpturing- which has been performed on the 
surface, and direct our inquiries to the nature of those more 
concealed agencies which seem to have exerted themselves 
somewhere within the solid crust of the planet. 

Movements of the earth's solid surface have been so 
often associated with volcanic phenomena that it is natu- 
ral that mankind from time immemorial should have 
ascribed mountain formation to the ao-encv of internal heat. 
The formation of mountains was, by the older geologists, 
considered explained by theories proposed to account for 
the phenomena of vulcanism; and there is unquestionably 
a close analogy between the seismic movements which 
often accompany vulcanic exhibitions, and the larger pro- 
cesses which have resulted in permanent mountain uplifts. 
Still, a slight consideration of the facts shows that the 
vast and systematic orographic convolutions of the terres- 
trial crust must have been produced by forces widely dif- 
ferent ill power and mode of action from the disturbing 
influences which result from igneous activities. There is 
reason, indeed, to consider whether these igneous manifes- 
tations are not, conversely, the result of movements in 
the earth's crust ; and this is a question to which we will 
return in connection with molten conditions and melting 
forces upon our planet. 

We will now proceed to give a concise exposition of 
the principal theories which have been promulgated re- 
specting the origin of mountains. 

1. Theory of Uphea/cal hy Aeriform Age)tts. — The 
idea that mountains have been uplifted, and terrestrial dis- 
turbances produced by steam, gases, or other heated agents, 
is as old as Strabo,* and may even be traced to Anaxa- 
goras,t who taught that earthquakes are ''produced by the 

*Strabo: Geographia, lib. vi. 

t Diogenes Laertius : Lives of the Most Illustrious Philosophers of Antiquity. 



OROGEi^IC FORCES. 293 

air which finds its way into the earth," An attempt was 
made to exphiin the origin of such mountain-raising agents, 
when Sir Humphrey Davy and others made appeal to 
chemical action as a source of heat, steam and gases. Sir 
Humphrey's arguments and experiments were in line with 
the current of new conceptions then flowing out of the 
new discoveries in chemistry, and for a time appeared 
extremely plausible. They were espoused by the dis- 
tinguished geologist Daubeney, and for some years they 
commanded very general credence. Reflection, however, 
produced the conviction that the cause was insuflicient in 
generalit}^, endurance and efliciency. Gas and steam-pro- 
duction through chemical action has not probably existed 
on a scale sufficiently vast to account for mountain-ranges 
thousands of miles in length and thousands of feet in 
height. And whatever the magnitude of gas or steam 
production, the causes operative have not probably been 
sustained through periods sufficiently prolonged. Such 
causes are seen to be operative in our times no longer; as 
they seem to have ceased to exist, there is no ground for 
affirming that they ever continued in action — if they ever 
existed — for such length of time as is required by a his- 
tory of mountain development stretching over £eons of 
geological time. It is conceivable, indeed, that agencies 
of this kind have had the requisite persistence, but the 
general condition of our planet has remained compara- 
tively unchanged through so many ages, while the evolu- 
tion of mountains has continued, that very little probability 
exists that the equilibrium of the chemical forces liad not 
been attained during the Archaean ages. But a further 
and more fatal objection to the present theory arises from 
the inadequacy of aeriform agents to do the work required. 
If mountains have been uplifted by steam or gases, those 
agents must have borne the weight of the mountains and 
overcome the resistances to motion presented by the rigidity 



294 A COOLIJ^G PLAi^^ET. 

of the rocks. This action has been necessary, not only to 
uplift the mountains, but to maintain them. Now, this 
work demands both improbable persistence and impossible 
energy. The steadiness of mountains is not maintained 
upon reservoirs of wind. Nor have gases or steam the 
unlimited power of reaction, even at the highest tem- 
peratures, which is implied in bea.ring the weight of 
the Andes or Himalayas. Such weights would crush 
them into fluid, viscid, and practically solid states.* 
These objections apply to the agency of the aeriform 
condition of matter however produced. Steam origi- 
nating from the penetration of surface waters to an 
assumed heated interior must be characterized by all the 
inadequacy of gases chemically originated. While, there- 
fore, the power of confined steam and compressed gases 
is immense, and may even contribute something to the 
phenomena of earthquakes, their elasticity is undoubt- 
edly limited far within the requirements of mountain 
formation. 

2. Theory of a Molten JVucleics and a WrinMing 
Crust. — If the primitive history of the matter of our planet 
has been such as set forth in the preceding portion of this 
work, there muso have been a time when incrustation be- 
gan, and there must have been a time w^hen matter in the 
liquid condition interposed a continuous zone between the 

* Compare Suess: Die Entstehung der Alpen, Wieii, 1875, abstract in Amer. 
t70Mr. /Sd., Ill, X, 446-51 ; Dana: Ma mi al of Geology, t\\\vCi edition, 747; Nature, 
xxi, 177, Dec. 25, 1879; J. D. Whitney, North American Revieiv, cxiii, 255. It 
was shown by Bischof in 1839, that " the elastic force of'steam cannot surpass a 
certain maximum, which it reaches when its density is equal to tliat of water;" 
and it has been calculated that this force would not in any case raise more than a 
column of lava seventeen miles high. The lacolitic mountains of Colorado are 
cases in which a moderate-sized mountain uplift seems to have been produced 
by the upward pressure of fluid hypogene matter : and this is the nearest approach 
known to mountain-making by a method of upburst. But these mountains are 
comparatively insignificant in dimensions, and there is no evidence of the inter- 
vention of the elastic force of vapors in their formation. (See G. K. Gilbert: 
Geology of the Henry Mountains, Powell Survey, 1877, Nature, xxi, 177.) 



OROGENIC FORCES. 295 

solidifying crust and the consolidated nucleus.* This was 
a time, too, when, according to the views entertained of 
nebular theory, the earth's rotation must have been much 
more rapid than at present, and the equatorial protuber- 
ance much greater. Thus, at the same epoch, the freedom 
of the protuberance to slip under the influence of nuta- 
tional and precessional forces, and the condition of greater 
efficiency in the action of those forces, were much more 
marked than in subsequent epochs, when the earth's mass 
became bodily rigid, and the oblateness was diminished. 
But passing by the possible climatic consequences of a 
shifting of the terrestrial crust in relation to the axis of 
rotation, I wish only to indicate here the grounds of the 
theory that the simple process of cooling may have devel- 
oped surface rugosities which grew into mountain magni- 
tude. 

The conception of wrinkling as an incident of terres- 
trial cooling seems to have been entertained by Descartes,f 
and was somewhat definitely enunciated by James Hall of 
Edinburgh, in 1812,1 M. Elie de Beaumont,§ Prof. Sedg- 

* Prof. James Hall says, nevertheless, that of the central mass of molten 
matter " we know notbing " (Pakeont. New York, III.) 

In a New York lecture of later date, before the American Institute, on the 
Evolution of the American Continent, he is reported to have said : "I desire to 
impress upon you this one truth, that we have not, in our geological investigation, 
succeeded in going back one step beyond the existence of water and stratifica- 
tion—one step toward this so-called primary nucleus of molten matter. * * * 
This original nucleus that has been talked about in geology has j)roclucecl no 
effect upon the surface of the earth ; neither upon its mountain chains or any 
other of the great features of the continent. (Report in Neiv York Trit)une.) 

t Descartes: Principes de la Philosophie, pt. iv, §§41, 42, 1644. Descartes 
gives several illustrative^figures, in one of which strata are shown uplifted and 
broken in a certain place, while on each side they are shown depressed. 

t James Hall, Trans. Roy. Soc, Bdinbnrgh, vii, 79, 1815, read, 1812. 

§De Beaumont: Les Systlmes de Monlagnes. Successive mountain up- 
heavals, in systems having each its own parallelism, "cannot be referred to 
ordinary volcanic forces, but may depend on the secular refrigeration of our 
planet.'' {Ann. des Sci. Nat., Sep., Nov. et Dec, 1829; Bevue Franqaise, No. 15, 
May, 1830; Bui. de la Soc. geol. de France, iv, 864, May, 1847.) 



296 A COOLIKG PLAifET. 

wick,* M. Constant Pr^vost,t and William Hopkins; J but 
the most effective scientific support of this doctrine has 
been traced out by more recent writers. The starting 
point of the theory is in the unequal rate of cooling of 
the superficial and deeply seated portions of the earth, and 
further, the unequal contraction of differently heated 
bodies when cooling from different temperatures. Physi- 
cal considerations have shown that some time after incrus- 
tation of a planet has begun, the rate of cooling at the 
surface will be somewhat slower than at some point beneath 
the surface, and that the surface may even retain a con- 
stant temperature, while the interior cools. § Mr. G. H. 
Darwin has recently shown that the actual seat of most 
rapid cooling in the earth is probably about 100 miles 
below the surface, and that this point continues to descend 
as cooling progresses. || It is also well known that the 
rate of contraction of a more highly heated body is more 
rapid than that of a body of lower temperature, when 
both cool the same number of degrees. Now, for both 
these reasons, the contraction of the interior of the earth 
must be more rapid than that of the cooler and less rapidly 

=!= Sedgwick, Trans. Geol. Soc, Lond.^ Jan. 5, 1831, in a paper on the .'struc- 
ture of the Cumbrian Mountains. 

+ C. Prevost, Sur la Thtor'ie des Soul'evemeiits, Bui. Soc. geol. de France, 
xi, 183, 1840, but taking a different view from de Beaumont. He ascribes the 
formation of mountains to '"tangential pressures propagated through a solid 
crust, * * * and produced by the relative rate of contraction of the nucleus 
and of the crust." 

XW. Hopkins, Address before the Geol. Soc. of Lond., 1853, Geol. Jour., ix, 
Ixxxix. 

§ Maxwell : Tlieory of Heat, 247 ; Sir W. Thomson, Trans. Roy. Soc. Edinb., 
1862; Thomson and Tait: Nat. Phil., App. D. See an jllustration of this prin- 
ciple by Rev. O. Fisher in Nature, xix, 173. M. Elie de Beaumont, applying 
Arago's observations on thermometers placed at various depths beneath the sur- 
face, to Poisson"s formulas embodying the mathematical theory of heat, calcu- 
lated that the epoch at which the cooling of the nucleus began to exceed that of 
the crust was .38,359 j'ears after the commencement of incrustation. Hence it 
might be inferred that this epoch determines the date of the commencement of 
the process of wrinkling. 

|! G. H. Darwin, Nature, xix, 313, Feb. 6, 1879. 



OROGENIC FORCES. 297 

cooling exterior layers. If, therefore, the exterior layers 
were perfectly rigid and infrangible, the interior would 
shrink away from the exterior, and open spaces would 
come into existence between them. But the nature of 
matter is such that a terrestrial film would be utterly inca- 
pable of sustaining its own weight if any adequate force 
were exerted to raise it into an arch having a span of some 
miles. The solid external film must therefore yield in 
some way so as to continue to rest generally, throughout 
its whole extent, upon the underlying nucleus. Under the 
enormous lateral pressure which would ultimately be de- 
veloped, the crust may be conceived as either crushing 
together, or undergoing a process of wrinkling and frac- 
ture, combined in certain proportions. Either of these 
consequences may be conceived as somewhat uniformly 
distributed geographically, or as localized to a certain ex- 
tent. The theory here considered supposes the result to 
take the form of wrinkling, and supposes it to be unequally 
distributed. If this conception represents the actual na- 
ture of the events, then wrinkles or folds of the planetary 
crust would arise which, in the course of ages, might 
naturally be conceived to grow into mountain dimensions. 
The process of wrinkling through the action of lateral 
pressure is finely illustrated by spreading a layer of clay on 
a stretched sheet of India rubber, and allowing the sheet 
slowly to contract.* The sheet may be five-eighths of an 
inch (16 mm.) thick, 6f inches (12 cm.) wide and 16 
inches (40 cm.) long. When stretched to 24 inches (60 
cm.) it may be covered with a layer of potter's clay from 
1 inch to 2f inches (25 to 60 mm.) thick, made as adher- 

* As first shown by M. Alphonse Favre of Geneva {La Nature, 1878), from 
whom the accompanying cut — one of four in La Nature,— has been borrowed. 
See also iVa^Mre, xix, 103, 1878, and also Rev. O. Fisher: Physics of the Earth's 
Crust, 128. In this connection the reader should also refer to the passage pre- 
viously quoted describing the cooling of a molten mass in the operations of a 
puddling furnace. See p. 219. 



298 A COOLIXG PLAXET. 

rent as possible to the India rubber, with a block of wood 
applied at eacli end. On the result shown in the annexed 
cut, several important observations may be made, (a) 
The strata are less contorted in the lower layers than in 
the upper, [b) The layers are disjoined in certain places 
by fissures or caverns, (c) They are traversed by clefts or 
faults inclined or vertical, (d) There is no sort of sym- 
metry in these structures, (e) The lateral pressure was 
exerted only from two opposite directions, and not as in 
the case of the earth's crust, from all directions ; and 
hence the folds reveal longitudinality or an axial dimen- 
sion. (/") The corrugations are distributed over the 
whole surface, and not accumulated in " chains " or groups. 
The importance of some of these observations will appear 
hereafter. 

The cooling and contraction which originate orographic 
wrinkles must be conceived as progressive and uniform. 
To a great extent, it may also be conceived, the evolution 
of mountain inequalities would be progressive and uni- 
form. But a moment's consideration of the unequal con- 
stitution and rigidity of the rocks, and especiall}^ the un- 
equal distribution of the firmest resistances to lateral 
pressure — especially after the primordial, fire-formed 
crust should have been once disturbed — renders it 
entirely probable that the progress of the development of 
surface inequalities would be somewhat spasmodic and 
convulsive. This theory, therefore, while recognizing an 
identity of forces and modes of action in ancient and 
later times, provides for any indications which may be 
discovered, of cataclysmic and revolutionary results of 
accumulated strains. It provides, also, for more energetic 
and more frequently recurring orographic activities in the 
earlier ages of the world than in the later. It also ex- 
plains why later mountain up-lifts should exceed the 
earlier in altitude, since, owino- to the increased thickness 



g 



OKOGEKIC FORCES. 



299 



and resistance of the crust, they 
could only have been produced 
after a longer continued and more 
highly intensified accumulation of 
strains. It is apparent, finally, that 
this theory, taken by itself, re- 
quires an immense number of 
comparatively short wrinkles run- 
ning in every conceivable direc- 
tion over the earth's surface, like 
the wrinkles in the skin of a shriv- 
elled apple. The theory provides 
no cause for a tendency toward 
determinate directions and pro- 
longed continuity in the wrinkles 
produced. But if mountains are 
developed from shrinkage wrin- 
kles, we must explain, also, why 
they are disposed in ranges and 
chains of ranges, and why they 
tend to sustain certain uniform 
relations to the meridian. The 
general theory of these phenom- 
ena has been already explained in 
a previous part of this chapter, 
and its particular application to 
the earth will be considered in the 
next chapter, when treating rather 
of existing phenomena than of 
antecedent conditions. 

The inauguration of a wrinkle 
would be the determination of 
lines of weakness, seen in cross 
section at a, ^, c. Figure 51, par- 
allel with each other. Evidently 






300 



A COOLTXG PLAXET. 



any continued tendency to wrinkle would be most readily 
developed along the existing wrinkle, since the lateral pres- 
sure B G would be resolved at G into the two components 
G I and G F, the latter tending to develop an elevation at 
G. The component G I would be again resolved into I L 
and I a. The downward stress I L would be opposed by 
the underlying matter, which w^ould contribute a part of 
its resistance along I a, and another part along I G. From 
the opposite direction. A, the lateral pressure w^ould yield 
a component tending to depress ^, and that, a component 
tending to elevate a. The two components meeting at a, 




Fig. 51. Formation of Wrinkles ix a Planetary Crust with Parallel 
Contiguous Furrows. Cross Section, 



would give a vertical or subvertical resultant a K. Thus, 
a wrinkle once inaugurated, further lateral pressure would 
tend to increase its elevation and deepen the parallel depres- 
sions. The weight and rigidity of the primitive fold «, finds 
always, ultimately, a component in the upward force G F, 
as explained, and this increases as the altittide and mass 
of a increase. In the course of time, therefore, accessory 
folds rise at G and H, separated from the main fold by the 
furrows h and c. In the later progress of these events 
the folds at G and IT repeat the action of the fold a. Thus 
parallelism of mountain ranges would result, the lateral 
ranges of course diminishing consecutively with increase 



OROGENIC FORCES. 301 

of distance from the central fold, and at the same time 
broadening their bases. 

The history of wrinkling must be regarded as begin- 
ning long before the descent of the ocean ; but it con- 
tinues through all the cooling geons of a planet's life. 
The ocean's waters would be accumulated to greatest 
depths in the deepest depressions between the wrinkles. 
When, after the measure of the oceans should be filled, 
the wrinkling should continue, the crests of the primor- 
dial wrinkles would be the first to emerge. Thus the 
germs of the continents, and afterward the continents 
themselves, would be stretched out in the places and in 
the attitudes predetermined before the ocean accumulated. 
The ocean basins and the ocean shores are conformed to 
the preconfiguration of the wrinkles. The location and 
trends of the mountain chains, therefore, have not been 
determined by the position of the ocean's mass, for the 
same cause has determined both. The ocean has pressed 
against the submerged slopes of the great folds, and to 
some extent has exerted an accessory lateral pressure. 
The effect of this, so far as it was felt, would be to 
increase the wrinkling effects and possibly (as Dana thinks) 
to incline the folds away from the coast line. 

The error must be avoided of conceiving the wrinkled 
condition of the planetary crust as restricted to the land 
areas.* Wrinkles would necessarily exist along many 
meridians on all sides of the planet. The ocean at first 
would cover all ; and only the highest folds and plateaux 
would ever emerge above the ocean level. There are 

*Rev. O. Fisher assumes (Physics of the Earth's Crust, 169, 179, 282, 283) 
that surface plications have not been developed under the sea. And yet he 
refers in another place {id., p. 78) to the fact that "contorted strata are to be 
also found, in what would be termed level countries, often covered with hori- 
zontal deposits of later date'"— for example, the highly contorted, carboniferous 
strata of parts of Belgium; and we might add, the contorted Archaean of Can- 
ada and New York, overlaid by horizontal uncontorted Potsdam sandstone and 
succeeding formations. 



302 A COOLI^^G PLAXET. 

mountains, valleys and plains in the bottom of the sea, as 
well as over the continents. The widest landscapes are 
buried beneath cubic miles of primitive brine.* 

Professor James D. Dana, whose thoughts on all sub- 
jects are suggestive and weighty, has devoted to the the- 
ory of mountains more study, probably, than any other 
American geologist ; and the whole subject of a shrinking 
globe and a wrinkling crust has been considered by him 
from every point of view.f Though his opinions in refer- 
ence to a fluid nucleus and the great influence of the 
ocean, and probably also, on the subject of "mashing 
together" (something to be presently explained) have 
been modified by the progress of investigation, he has 
always maintained that "the principal mountain chains 
are portions of the earth's crust which have been pushed 
up and often crumpled or plicated by the lateral pressure 
resulting from the earth's contraction ; " that the oceanic 
areas have been "the regions of greatest contraction and 
subsidence, and that their sides have pushed like the ends 
of an arch, against the borders of the continents," deter- 
mining the border position of orographic and volcanic 
phenomena ; that metamorphism has taken place only 

*See the section from Charleston, S. C, across the Gulf Stream, by A. D, 
Bache, Froc. Amer. Assoc, 1854, 141, and Diagram 9. But Bache's conclusions 
are not confirmed by Commander J. K. Bartlett, Bulletin Xo. 2, Amer. Geo- 
graph. Soc, p. 73, 1882. For the general configuration of the Atlantic bottom, 
however, see C. Wyville Thompson : Voyage of the Challenger; Depths of the 
Sea, etc. On the configuration of the bottom of the Pacific, see J. D. Dana, 
Sep. Geol. Wilkes U. S. Expl. Exped., 4to, 1849. p. 339, and Corals and Coral 
Islands, 8vo, 1872, p. 329. 

t See a summary of Professor Dana's views in Amer. Jottr. Set., Ill, v, 423-5, 
with references to numerous earlier publications by himself. The article here 
referred to is an extended memoir embracing his final conclusions On some- 
results of the Earth's Conti action from Cooling, including a discussion of the 
Origin of fountains and the Nature <f the Earth's Interior, Part I, Review of 
opinions, and Theory of ^fou tain Origin, 423-43, June, 1873: Part II, Condition 
of the Earth's Inteiioi; and connection of Facts with Mountain-making, and 
Part III, Metamorphism, id. Ill, vi, 6-14; Part IV, Igneous Ejections, vi. 104-6; 
Part V, Formation of Continental Plateaux and Ocean Depressions, vi, 161-72, 
Sep., 1873. See, also, Dana's Manual of Geology, 3d edition. 



OROGEIs^IC FORCES. 303 

during periods of disturbance, and he now thinks that the 
heat required has been derived partly from the earth's 
liquid interior and partly from the crushing strains (see 
beyond) experienced by the crust. He maintains that 
wide areas have experienced geosynclinal and geanticlinal 
movements, and that the latter are not accompanied by 
plication and metamorphism, though they sometimes 
attain low mountain altitudes, a^d supplement the eleva- 
tion of characteristically plicated and metamorphic 
mountain chains. 

The theory of wrinkling over a molten interior, or even 
a fluid zone, has been objected to by Professor Joseph Le 
Conte* on the ground that the materials of the crust do 
not possess sufficient rigidity to sustain themselves much 
above or below the plane of fluid equilibrium. Hence the 
great folds of mountains and the broader arches of conti- 
nents and plateaux, as well as the depressions of the 
ocean basins, cannot be regarded as the simple phenomena 
of wrinkling; and Professor Le Conte, like Archdeacon 
Pratt t and Robert Mallet,]; refers these unequal saliences 
of the crust to unequal radial shrinkage. For some rea- 
son, as he thinks, the earth has contracted more along the 
radii under the depressions than along those under the 
elevations; and the earth has attained sufficient rigidity to 
sustain the pressure resulting from such inequalities. § 
But great elevations and subsidences, and even mountain 
folds, are known to have been produced when the circum- 
stances are such as to prove that the terrestrial crust 

* A Theory of the Formation of the Great Features of the Earth's Surface, 
Amer. Jour. Sci., Ill, iv, 345, Nov., 1872. 

+ Pratt: Figure of the Earth, 4th ed., 200, 206, 1871, 

X Mallet, Trans. Roy. Soc, 1873, §§ 52, 60. Principal J. W. Dawson seems 
to entertain n similar view, as indicated in his Address in Science, ii, 197, Aug. 
17, 1883. 

§Rev. O. Fisher, however, has shown that the whole radial contraction 
would not equal the difference of level between the land surface and the sea 
hottom.—Physics of the Earth's Crust, 79. 



304 A COOLING PLAXET. 

possesses sufficient rigidity to sustain the saliences, and 
sufficient hypogeal mobility to permit them sometimes to 
return to older positions. Thus, as Professor J. D. Dana 
has reminded us,* the region about Montreal and thence 
to Lake Champlain and the coast of Maine has been raised 
without evidence of plications from 200 to 500 feet in 
late Post-Tertiary time; and some of the higher regions 
of the Rocky Mountains have been raised 8,000 to 10,000 
feet since the Cretaceous age, and there is uo reason to 
suppose that any disturbances revealed in the Cretaceous 
and Tertiary strata have been the cause of the elevp.tion. 
In other instances, as in the AUeghenies, the Uinta and 
the Sierra Nevada, as shown by Lesley, Powell and King, 
enormous downthrows have taken place, to the extent of 
10,000 to 25,000 feet; and these are most naturally explic- 
able on the theory of folds and arches in the earth's crust. 
In fact, it is a common thing to find a hne of fault passing 
into a fold or flexures, as for instance, in the region of the 
High Plateaux of Colorado. It is scarcely conceivable 
that the flexure-continuation of a fault should not be sus- 
tained by its own strength over some mobile condition of 
matter ready to retreat as soon as the strain becomes too 
great for the material to withstand. The continuity of 
folds and faults is well illustrated in the experiment of 
Favre, previously described. 

That folds and arches actually exist, and not merely 
elevations caused by crushing together, and that such 
folds or wrinkles w'ould arise upon the surface of an 
incrusting globe is a conclusion so well sustained by facts 
and opinions that we may venture the assertion that the 
difficulty raised by Professor Le Conte is not a very serious 
one. 

Captain C. E. Button has urged an objection which is 
more recondite. He questions the adequacy of contrac- 

* Dana; ResuUs of the Earth's Contraction, Anier. Jour, Sci., Ill, v, 428. 



OROGEXIC FORCES. 305 

tion to develop the rugosities of the earth's crust. Start- 
ing from Fourier's solution of the problem of the '' rate of 
variation of temperature from point to point, and the 
actual temperature at any point in a solid extending to 
infinity in all directions, on the supposition that at an 
initial epoch the temperature has had two different con- 
stant values on the two sides of a certain infinite plane," 
and using Sir William Thomson's application of the solu- 
tion to the case of the earth. Captain Button finds that 
on any supposition as to present rate of increase of tem- 
perature downward, and as to the conductivity of the 
rocks, "the greatest possible contraction due to secular 
cooling is insufficient in amount to account for the phe- 
nomena attributed to it by the contractional hypothesis." 
"By far the larger portion of this contraction," he says, 
"must have taken place before the commencement of the 
Palaeozoic age. By far the larger portion of the residue 
must have occurred before the beginning of the Tertiary; 
and yet the whole of this contraction would not be suffi- 
cient to account for the disturbances which have occurred 
since the close of the Cretaceous." 

Captain Button thinks, also, that "the determination 
of plications to particular localities presents difficulties in 
the way of the contractional hypothesis which have been 
underrated." The localization of the plications is only 
possible on the assumption of a large amount of horizon- 
tal slipping of the crust over the nucleus_, and this would 
present, even over a liquid nucleus, an amount of friction 
which renders the assumption a physical absurdity.* 
Wrinkling resulting from uniform cooling, and, conse- 
quently, uniform shrinkage, would be represented by the 
analogy of a withered apple, instead of a surface present- 

*C. E. Dutton, Amer. Jour. ScL, viii, 113-23, Aug., 1874. See also Penn. 
Monthly, May and June, 1870, on Theories of the Earth's Physical Evolution, 
and Geol. Mag., Decade ii, Vol. iii, 327, reviewed in Geol. Mag., iv, 322. 
20 



306 A COOLIES G PLANET. 

ing in one region one continuous system of plications 
extending from Cape Horn to Behring's Sea, and in an- 
other, a zone a thousand miles in width, from the Appa- 
lachians to the one hundredth meridian, with almost no 
evidences of disturbance presented. 

Rev. O. Fisher has also made objection to the contrac- 
tional theory.* While admitting that the crumpling of 
the earth's crust reveals the action of lateral pressure, he 
shows by calculation based on certaiji assumptions of con- 
stant quantities, that the elevations above a datum plane 
due to the contraction of a solid earth, would not form a 
layer exceeding nine hundred feet in thickness, while the 
actual elevations above the same plane would form a layer 
ten thousand feet in thickness. The compression, there- 
fore, must be due to some other cause than contraction of 
the earth through loss of heat. He, therefore, attempts 
to establish the probability that the crust rests on a fluid 
zone in a state of igneo-aqueous fusion, and that the escape 
of steam and gases into fissures formed on the under side 
of the crust exerts the lateral jDressure which has contorted 
the strata. 

Captain Button's assumption that the contractional 
theory implies a molten nucleus enables him to argue that 
at the beginning of incrustation the whole earth had cooled 
nearly to the point of solidification. But, it may be held, 
as it is generally held, that the terrestrial nucleus began to 

* O. Fisher : Physics of the Eai th's Crust, ch. iv. London, 188L Mr. Fisher's 
views on vulcanisra and orogeny have mostly appeared in previous periodical 
publications. See, especially, Oa the Elevation of Moifntain Chains by Lateral 
Pressure, Trans. Cambr. Phil. Soc.,xi. PartH, 18; Part III, 489, 1868; On Elevation 
and Subsidence, Phil. Mag., 1872 ; On the For7nation of Mountains and the Hi/poth- 
esis of a Liquid Substratum beneath the Earth's Crust, Proc Cambr. Phil. Soc, 
Feb. 22, 1875; Mountain-making ; The Inequalities of the Earth's Surface Viewed 
in Connection with Secular Cooling, Trans. Cambr. Phil. Soc, xii. Part I, 505: 
PartIL 431, abstract in Amer. Jour. Sci., Ill, x, .389-90: Remarks njjon Mr. Mol- 
let^s Theory rf Volcanic Energy, Quar. Jour. Geol. Soc, London, sxxi, 469-78, 
May 12, 1875; Mr. Mallet's Theory of Volcanic Energy Tested, Phil. Mag.. IV, j, 
302-19, Oct., 1875; id. V, i, 138-42. 



OKOGENIC FORCES. 307 

solidify at a temperature much above the point of liquefac- 
tion under atmospheric pressure. If so, the process of 
equalization of temperature by convection could be carried 
on only in the region exterior to the consolidated nucleus, 
and when incrustation began, a very high temperature was 
shut up in the nucleus. A greater amount of cooling and 
contraction must therefore take place than would be pos- 
sible on Captain Button's assumption of a liquid nucleus 
at a lower temperature. Moreover, Captain Button as- 
sumes, with Sir William Thomson, that as fast as surface 
materials solidified, they would sink by their increased 
density into the fluid mass, until the late-formed and com- 
paratively cooled solid nucleus should have grown nearly 
to the surface. This would be an additional cause of gen- 
eral reduction of internal temperature. But the theory of 
a sinking crust can scarcely stand, in the light of recent 
researches, already cited, on the relative densities of freshly 
solidified masses, and the molten magmas from which they 
were derived. It is much more probable that incrustation 
began at an early stage, and at once began to arrest escape 
of internal heat, so that since the first incrustation, the in- 
terior has undergone a larger amount of shrinkage than 
Captain Button admits.* Still, it must be borne in mind 
that an initial temperature of 7000° Fahr. is assumed, and 
this is probably 3000° above the melting temperature of 
silicious rocks under atmospheric jjressure. Undoubtedly, 
the results exhibited by Captain Button and Rev. Mr. 
Fisher respecting the inadequacy of all probable contrac- 
tion through cooling, to develop the necessary tangential 
pressure, must be very carefully considered. But while 
the effects of contraction remain too clearly indicated to 
be mistaken, and while all admit, as they must, that some 
contraction must have resulted from cooling, it seems ra- 

* Compare remarks by A. H. Green, Nature., xxv, 481, relative to the initial 
temperature of 7000°. 



308 A COOLIXG PLAXET. 

tional to maintain that the theoretical estimates of the 
results of possible contraction are vitiated by some unde- 
tected errors in the principles assumed or the constants 
employed. 

As to Captain Button's objection that the formation of 
a mountain range is impossible upon a globe contracting 
equally along all its radii, this seems well taken, and I 
know of no wa}^ to meet it on principles generally recog- 
nized by geologists. As to myself, however, I am at once 
reminded of the tidal influences already discussed. Here- 
after, in treating of the physiographic features of our 
planet, I shall point out the remarkable correspondences 
between the orographic trends and the structural lines 
which I believe must have been wrought by tidal action in 
the primitive crust. I strongly believ^ that in this is to be 
found the only explanation of the difficulty suggested. 

As to the improbability of the requisite slipping of the 
crust to develop mountain ranges along certain meridians, 
with broad continental plains intervening, I am inclined to 
disagree with Captain Button. With an underlying liquid 
or plastic layer nearly or quite continuous, and meridional 
predispositions and lines of weakness preexisting, it seems 
to me probable that regions of sound crust unaffected by 
any predisposition to folding, would possess sufficient 
rigidity to undergo the requisite local translation, and to 
press with the requisite force against rising folds, and even 
to press their bases under and cause their summits to over- 
hang toward the continental side — a result exhibited re- 
markably in the Alps, where the pressure from both sides 
has been such as to develop overhanging in both directions 
from the centre, producing the well known fan-shaped 
structure. This is admirably seen in a section across 
Mont Blanc, where the Jurassic strata and underlying 
crystalline schists of Val Veni have been overturned 
toward the south, and the same formations in the valley of 



OROGEKIC FORCES. 309 

Chamounix have been overturned toward the north, while 
the central protogine mass rests like a protruded bulge be- 
tween the two sets of schists. Hard by in the Brevent, 
the crystalline schists have again been squeezed to a verti- 
cal attitude, but the protogine was not forced up in the 
middle. The contracted base of a great terrestrial fold is 
also seen in the St. Gotthard mass, included in the accompa- 
nying section through the Alps. The restored folds of this 
section, indicated by the dotted lines, convey irresistibly the 
impression of action from the sides. (See next page.) 

The probability of crustal slipping is expressly recog- 
nized by Dr. Dawson, who, speaking of past movements 
of the earth's crust, says : * " One patent cause is the 
unequal settling of the crust toward the centre; but it is 
not so generally understood as it should be, that the 
greater settlement of the ocean bed has necessitated its 
pressure against the sides of the continents in the same 
manner that a huge ice-floe crushes a ship or a pier. The 
geological map of North America shows this at a glance, 
and impresses us wath the fact that large portions of the 
earth's crust have not only been folded, but pushed bodily 
back for great distances,^"^ 

The pressure from the continental side of a fold should 
establish a relation between the height of a mountain-fold 
and the breadth of the continental area which has not been 
affected by the plications due to it, but which have been 
accumulated along its borders. In any event, the folds 
exist, and however caused, the same necessity of slipping 
over uncorrugated areas would arise. f 

But finally, when we contemplate the physical situation 

* J. W. Dawson, address at Minneapolis, as retiring president of the Ameri- 
can Association, Science, August 17, 1883. Quoted only for the passage itali- 
cised, since the cause assigned would not tend to produce the effect alleged, but 
rather a wrinkling of the ocean bottom. 

t Tlie evidences of pressure from the continental side are recognized in the 
White Mountain region by C. H. Hitchcock {Geol. of New Hampshire, i, 519). 



310 



A COOLIXG PLA^'ET. 




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onoGTiNic i?oiicEs. 311 

ill that " analytic spirit " which Captain Button recom- 
mends, it is apparent that tlie question of slipping does 
not properly arise. By hypothesis, the crust is underlaid 
by a liquid zone or a liquid nucleus. The shrinkage of 
the nucleus develops the lateral pressure in the crust; and 
the surface of the shrinking nucleus has all the motion 
here attributed to the crust, though less localized. The de- 
termination of the parts of the crust to yield to the pres- 
sure depends only on the location of the weakest regions. 
Points in the crust adjust themselves in position accord- 
ingly. If any friction arises between the crust and the un- 
derlying fluid, the fluid being free to move, moves with the 
crust, and the resistances offered to the adjustments result- 
ing from relief from pressures of inconceivable magnitude 
are too inconsiderable to be mentioned in this connection.* 
The expedient by which Mr. Fisher attempts to pro- 
vide the requisite amount of tangential pressure in default 
of adequate contraction, is certainly original, if not a 
heavy strain upon credulity. Should the assumed state 
of igneo-aqueous fusion be granted, and should the exist- 
ence of innumerable fissures be also granted, in a crust 
already so squeezed by contraction as to close every open- 
ing, it is still extremely difficult to admit that the penetra- 
tion of the fissures by elastic vapors furnishes an adequate 
cause for mountain corrugations. As before stated, the 
utmost energy of confined vapors is insufficient to raise 
the mountains and crush the crust. Movements of eleva- 
tion, moreover, have been slow, persisting through geo- 
logic geons; these are not the characteristics of the action 
of elastic vapors. f 

* If Captain Button will turn to Baltzer's Der GUirnisch ein Problem Alpinen 
Gebirgsbaues, he will find a section which, under the interpretation given, de- 
monstrates extensive slipping, not only over a liquid magma, but over older and 
consolidated formations; and not only slipping, but an amazing system of folds 
afifecting, for instance, the Cretaceous and Eocene strata, without corresponding 
folds in the Jurassic and Triassic strata. 

t Compare the criticisms of A. H. Green, Nature, xxv, 481, March 23, 1882. 



312 A COOLIXCt plaxet. 

The theory of lateral pressure through nuclear contrac- 
tion is accepted in its general features by Professor 
Albert Heim of Zurich,* one of the most thorough and 
competent investigators of recent times. Heim, however, 
to the contractional theory adds a subsidiary hj'pothesis. 
He holds that the great pressure exerted on the deeper 
strata, say below 3,000 meters, reduces them to a plastic 
state. Thus, while the overlying more recent sediments 
attain and retain real rocky rigidity, the crystalline schists 
acquire a condition in which lateral pressure more readily 
develops folds and plications. Thus it often happens that 
movements of the crumpling deeper strata carry the rigid 
overlying strata b}" a slipping movement over considerable 
distances, until the accumulated strain results in a local 
fold of the newer and more rigid strata, as in the remarka- 
ble case of the Glarnisch section described by Baltzer. 
Dr. Friedrich Pfaff of Erlangen,f however, argues against 
the hypothesis of deep plasticity, maintaining that the 
deepest portions of the earth would, on this theory, be the 
most fluid, and the earth would thus be destitute of the 
rigidity demanded by astronomical conditions. He main- 
tains further, that mountain phenomena are such as de- 
mand rigidity for the explanation of upheaval and fold- 
ing, since plastic masses are shown by experiment to yield 
quite different phenomena, both when pressed and when 
exerting pressure. 

Dr. Pfaff, after a careful examination of the contrac- 
tional theory, concludes that it is inadequate to explain 
certain phenomena of mountain formation. His objec- 
tions may be stated as follows: (1) Cooling would not neces- 
sarily produce the requisite contraction. If it should 
do so, there is implied (a) A temperature in the fluid in- 

*Heim: Untei^suchungen iiber den Mechanisnius der Gebirgsbildung, 2 vols. 
A work embodying the results of long and tireless research. 

+ Pfaff: Der- Mechanisnius der Gebirgsbildung, 8vo., 143 pp., 1880. 



OROGENIC FORCES. 313 

terior much higher than the melting- point of rock, and at 
the same time, {b) A cooling of the interior much more 
rapid than that of the surface. These two implications 
conflict, as he thinks, with each other. (2) The whole 
thickness of the crust must have sufl:'ered folding simulta- 
neously, and this, in some cases, is not the fact, since the 
upper or lower formations have been separately folded. 
(3) The folds are localized instead of being generally dis- 
tributed over the surface. (4) The folds extend in long 
ranges of determinate direction, instead of being promis- 
cuously disposed. (5) The newer formations have received 
more extensive folds than the older, whereas progressive 
cooling should result in progressively diminishing contrac- 
tional results. The second, third and fourth objections 
are considered the most serious. 

As to Dr. Pfaff's first objection, I think it loses its force 
in view of general considerations heretofore presented. 
As to the second, we may admit that the whole crust 
would be subjected to similar action, but we might rea- 
sonably expect the visible results to be differently devel- 
oped in formations of different constitution and rigidity, 
and acted on by different superincumbent pressures. 
Deep-seated plasticity, for instance, as Heim suggests, 
may be reasonably conceived a true explanation of discord- 
ant movements in the upper and the deeper portions of the 
crust; though the plasticity supposed need not be attrib- 
uted solely to pressure, but partly to the effect of heat 
and water in a zone more shallow than that where com- 
pression results in solidification. As to the third and 
fourth objections, they will be recognized as identical with 
certain ones urged by Captain Dutton, and their removal 
results, as I have shown, from the recognition of the 
effects of tidal action on an incrusting planet. As to the 
fifth objection, it seems to assume that the newer forma- 
tions have been more disturbed because they have been 



314 A COOLIXG PLAKET. 

wrought into larger folds. There is no other evidence. 
But the premises of the objection probably invert the 
facts. The older strata have been most disturbed. But 
in the earlier and thinner condition of the crust, lateral 
pressure developed more numerous plications and a greater 
amount of crushing; in the later condition, increased 
rigidity resisted pressure until the strain accumulated to 
such an extent as to evolve movements more extensive 
vertically, though much less numerous. 

Dr. Pfaff, however, chooses, for the present, to set aside 
the contractional theor}", and in its place offers the 
hypothesis that large quantities of water finding their way 
into the crust, by some means which he does not explain * 
excavate vast cavities, and that the subsidence of the over- 
lying strata gives rise to the dislocations which thus affect 
the upper and not the deeper portions of the crust. It 
does not seem to occur to Dr. Pfaff that this hypothesis 
involves greater difficulties than the theory for which it is 
proposed as a substitute. 

The theory of mountain origin through Avrinkling of 
the crust ma}^ suffice to explain elevation, volcanic and 
seismic actions, and even metamorphism and plications; 
but there are two characteristics of mountain corrugations 
^vhich this theory cannot explain. These are the great 
thichenhig of the formations involved in the corrugations, 
and the greatly increased fragmented condition of the 
sediments. To supjjly these deficiences in orogenic theory 
other speculations have been promulgated, which I will 
now concisely explain. 

3. Theory of Copious Sedhnen.tation along Geosyn- 
clinaU. — In 1857, Professor James Hall, in a presidential 
address before the American Association at Montreal, 
enunciated the doctrine that the enormous thickening of 

*"Wirpincl bis jetzt allerdiiigj! iiicht iin Stantle, dariiber genaue Auskanft 
zu geben, wir Wigsen imr, daswasser in die grossten Tiefen hinabdringt, aber 
nichts Sicheres iiber seine Wirkung daselbst.'"— Op. cit., 119. 



OROGEKIC i?ORCES. 315 

the formations along the Appalachian chain was due to 
the prolonged accumulation of sediments along a sinking, 
off-shore line of sea-bottom. The study of the Appala- 
chians and other American mountain regions led him to 
the enunciation of a general theory, of which the princi- 
pal points are the following: Coast regions are the courses 
of marine currents, and hence of deposited sediments. 
The accumulation of sediments by their gravity gradually 
sinks the crust, and thus a great thickness is attained; 
the rocks become solidified and crystallized below. The 
continents are afterward somehow raised — not the moun- 
tain regions separately. The mountains are shaped 
out of other sediments by denudation — as James Hutton 
had previously argued. Metamorphism is due to "mo- 
tion," '* fermentation" and a little heat — the last coming 
up from below in consequence of the increasing accumu- 
lations at the surface."^ A summary of these views, and 
to some extent, a commentary on them, was published by 
Dr. T. S. Hunt, in 1858. f Dr. Hunt entertains generally 
the same views as Professor Hall, and indeed preceded 
him in the conception of a softened plastic zone in a state 
of igneo-aqueous fusion, situated between the consolidated 
crust and the solid nucleus; though he was also preceded 
in this by Keferstein]; and Sir John Herschel.§ Dr. Hunt 
places greater stress than Professor Hall on the influence 

* Prof. Hall's address is published only in the Introduction to vol. iii, Pa- 
laeontology of New York. [By a resolution of the Standing Committee of the 
Association, in August, 1882, the address is to be published by the Association, 
after an interval of twenty-five years.] See criticisms by J. D. Dana, Amer. 
Jour. Sci.,n, xlii, 205-11. 

•IT. S. Hunt, Canadian Journal, March 7, 1858; Quar. Jour. Geol. Sci., 
Nov., 1859; Amer. Jour. Sci., TI, xxxi, 411. See, also, correlated views in .itner. 
Jour. Sci., 11., 1, 21, and Geol. Mag., June, 1869, on The Probable Seat of Volcanic 
Action; also, Amer. Jour. Sci., Ill, v, 264-70. Prof. Hall's theory is in part 
accepted by Geo. L, Yosc in Orographic Geology, 186(5, 47-55. 134. 

^Keferstein: Naturgeschichte des Erdkorpers, 1834, vol. i, 109; Bull. Soc. 
geolog. de France, I, viii. 19"(. 

§ Sir John Herschel, Proc. Geol. Soc, London, 1836, ii, 548; Babbage's Ninth 
Bridgeivater Treatise, Note I, 225-57. 



316 A COOLIls^G PLAXET. 

of softening. He conceives the most important result of 
the subsidence to be, to "cause the bottom strata to estab- 
lish lines of weakness or of least resistance in the earth's 
crust, and thus determine the contraction which results 
from the cooling of the globe to exhibit itself in those 
regions, and along those lines where the ocean's bed is 
subsiding beneath the accumulated sediments." While 
Professor Hall had conceived the process of subsidence as 
the principal cause of the corrugations of the strata, Dr. 
Hunt regarded the subsidence rather as the occasion which 
determined the position and direction of the corrugations, 
while the cause of the displacements and metamorphism 
was the contraction of the earth's nucleus, and of the 
deep-seated sediments themselves. 

Professor Joseph Le Conte has entertained a similar 
view* as to the cause of subsidence. "Suppose," he 
says, "sediments accumulating along the shores of a con- 
tinent, the first effect is lithification, and therefore, increas- 
ing density, and therefore, contraction and subsidence, 
'pari]yo.8Su with the deposit. Next, if the sedimentation 
continues, follows aqueo-igneous softening, or even melt- 
ing, not only of the lower portion of the sediments them- 
selves, hut of the underlying strata upon ichieh they were 
deposited. The subsidence probably continues during 
this process. Finally, this softening determines a line of 
yielding to horizontal p)ressure^ and a consequent upswell- 
ing of the line into a chain. Thus are accounted for, 
first, the subsidence, then the subsequent upheaval, and 
also the metamorphism of the lower strata so universal in 
great mountain chains" (p. 468). f Professor J. D. Dana 
attributes the subsidence chiefly, at least, to lateral pres- 

* J. Le Conte, A Tlieoi^j of the Formation of the Great Features of the 
Earth's Surface, Amer. Jour. Sci., Ill, iv, 345-55, 460-72, Nov. and Dec, 1872. 

t Subsidence under weight of sediments is recognized by J. S. Gardner and 
Dr. Charles Ricketts in communications to the GeologFcal Section of the British 
Association in \%'ii.— Nature, xxvi, 468, 469, Sept. 7, 1882. See, also, note p. 334, 



OROGEN^IC FORCES. 317 

sure. He holds distinctly, also, to a real local elevation of 
the crust along a mountain geosynclinal, at the end of the 
subsidence, attended by plication and metamorphism. He 
holds also, that real elevations occur sometimes without 
plication and metamorphism.* 

This theory offers a probable explanation of the aug- 
mented thickness of mountain formations,! but physical 
geologists will scarcely indorse the presumption that the 
formation of a geosynclinal is due to an accumulation of 
sediments. It is indeed, frequently asserted that delta 
regions are generally in process of subsidence under the 
weight of deposits; but it is scarcely 'credible that a crust 
possessing sufficient rigidity to sustain the weight of moun- 
tains, would be subject to depression under the load of a 
few feet of sediments buoyed up by immersion in the sea];. 
Moreover, Mr. Clarence King has shown§ that subsidence 
has in some cases accompanied unloading of sediments, 
and the accumulation of sediments has been attended by 
upheaval. The theory apparently inverts the relative 
positions of cause and effect.] If, however, subsidence 
from nuclear contraction or any other cause is taking place 
along a shore, this depression will naturally determine the 
place of excessive accumulation of sediments, especially 
if an ocean current corresponds in position and direction. 

* Dana, Results of the Earth's Contraction, Amer. Jour. Sci., Ill, v, 423 43, 
June, 1873, continued, ib., vi, 6-14, 104-6, 161-72. 

tProf. J. D.Whitney ascribes the thickening of the formations reposing 
along the flanks of a granite axis to the denudation of this axis after upheaval in 
the midst of the ocean. (J. D.Whitney: Mountain Building. Also, North 
American Review, cxiii, 235-74.) How high must the axis have been to supply 
the requisite amount of sediments in any average case? 

i Compare Fisher, Geographical Magazine, x, 248. 

§ King : Geology of the kOth Parallel, i, 357, 732. 

ii Nevertheless M. Faye attributes even greater effects to accumulation of 
burdens upon the ocean's bottom. This depression of the sea- bottom is recip- 
rocated, he thinks, by the elevation of continents and mountain chains. To the 
weight of sediments, however is added, on his theory, the effect of increased 
thickening of the cooled crust under the ocesux.— Faye, Annuaire du Bureau 
des Longitudes, 1881. 



318 A COOLIXG PLAXET. 

This theory also explains the coarsely fragmental 
character of the deposits, especially if the depression is 
overflowed by an ocean current bringing sediments from a 
crumbling coast, as was suggested by Professor Hall, who 
posited a wasting continent to the northeast of the Ap- 
palachian geosynclinal. 

The theory is unsatisfactory, however, on two additional 
points. Perhaps it should be said the theory is incom- 
plete. It does not offer an adequate explanation of moun- 
tain saliences. That some mountains are strictly results 
of neighboring erosions cannot be doubted. Nor is it 
easier to doubt that others have originated through 
some sort of local elevation. Very few Americiin or 
European mountains indicate by their structure that they 
are mere remnants of wasted continents. The dips of the 
strata flanking them almost universally demonstrate that 
uplifts have taken place which have inclined the sheets of 
sediments along each side. Xor does the theory offer an 
adequate explanation of the enormous amount of plication 
and crumpling which generally accompany mountain forms. 
It seems to conceive the synclinal trough filled by sedi- 
ments to a state of convexity and so maintained while 
slowly sinking. The sinking process effects the plication. 
Now the plication, in many cases, amounts to at least twice 
the horizontal extent of the formation, and this would re- 
quire in a synclinal twenty-five miles wide, a vertical alti- 
tude of fifty miles. In any ordinary case of crumpling or 
plication, the altitude must have been equal to the breadth 
of the synclinal, or so nearly equal to it as to annihilate 
all presumption in favor of the theory. Dr. Hunt joins to 
this action the secular contraction of the earth's nucleus, 
and Professor J. Le Conte, Professor J. D. Dana and others 
assign secular contraction alone as the cause of plications 
along a filling geosynclinal. The latter two also main- 



OROGEJs-IC FORCES. 319 

tain that the plications were produced chiefly at the end 
of the process of subsidence. 

4. Theory of Mashiiuj Together. — In 1872, Mr. Robert 
Malletj an eminent English engineer, propounded* the 
theory that the secular contraction of the earth's nucleus 
had developed tensions in the crust, which found relief in 
the local crushing of the rocks along lines of relative weak- 
ness, and thus heat was evolved by transformation of me- 
chanical energy. Mr. Mallet, however, maintained that in 
the earlier condition of the earth, while the crust was thin- 
ner, tangential thrust had developed mountain folds, where- 
as, in modern times, it develops chiefly vulcanic and seismic 
phenomena. He substantiated his theory by a citation of 
many results of the experimental crushing of rock frag- 
ments, and calculated that the total heat escaping through 
volcanic vents is fully accounted for by the thermal effects 
of the secular crushing of the crust, while the normal 
radiation is supplied by slow conduction from the primi- 
tively heated interior. Mr. Mallet subsequently enforced 
these views by many observations, experiments and calcu- 
lations.f 

* Mallet, Volcanic Energy, an Attempt to Develop Us True Origin and Cos- 
mical Relations, Proc. Roy. Soc, No. 136, 1872, Phil. Trans., 1873, pt. i, 147, ab- 
stract in Amer. Jour. Sci., Ill, iv, 409-13; vii, 145-8; additions to this, Phil. 
I'rans., 1875, clxv, pt. i, abstract in A^ner. Jour. Sci., Ill, viii, 140-1. For criti- 
cisms and comments on Mallet's theory see Sir William Thomson, Nature, Jan. 
18 and Feb. 1, 1872 (compared with which see J. G. Barnard, Smithsonian Contri- 
butions, No. 240, and Sir W. Thomson's later publications, with modified views); 
D. Forbes, Nature, Feb. 6, 1872; F. W. Hutton, Nature, Nov. 27, 1873; E. W. 
Hilgard, Amer. Jour. Sci., Ill, vii, 535-46, June, 1874, and Phil. Mag., July, 1874, 41. 

t Robert Mallet, On the Temperature Attainable by Rock-crushing, and its 
Consequences, Phil. Mag,, July, 1875, 1-13, and Amer. Jour. Sci., Ill, x, 256-68, 
xii, 463; Phi!. Mag., V, i, 19-22. See, also, Mr. Mallefs Introduction to L. 
Palmieri's work on the Eruption of Vesuvius in 1872, entitled. On the Present 
State of Knowledge of Terrestrial Vulcanidty, the Cosmical Nature and Rela- 
tions of Volcanoes and Earthquakes, abstract in Amer. Jour. Sci., Ill, v, 219-25. 
Numerous other publications by Mr. Mallet bearing more particularly on the 
science of volcanoes and earthquakes may be found in Tranx. Roy. Irish Acad., 
1848; Reports to British Assoc, 1850. 1851, 1852, 1853, 1854, and Trans. Brit. 
Assoc , 1857-8; The Great Neapolitan Earthquake of 1857, Svo, 1862, pt. iii; Phil. 
Trans., 1862, and Amer. Jour. Sci., Ill, v, 302. 



320 A COOLIXG PLAXET. 

It ought to be mentioned that Professor Wurtz, as 
early as 1866, advanced kindred ideas.* He referred to 
"the tremendous dynamic agencies whose effects of up- 
heaval, subsidence, disruption and displacement we find 
so widely manifest. [These] while doubtless themselves 
engendered of the pent-up heat-energy of the interior, 
must have given birth to, or have been in part transmuted 
into, heat-motion. Hence I deduce two conclusions of 
great moment, but one or two of which can now be dwelt 
upon. It follows, for instance, that in our theoretical 
views of metamorphism, we are by no means of necessity 
limited for our essential chemical excitant, merely to that 
portion of the hypothecated residual cosmical heat which 
might be supposed to have been retained by the emerging 
ocean floor. Neither elevation nor subsidence (both neces- 
sarily accompanied by enormous compression) could occur 
without rise of temperature." * * * In a note he in- 
quires, "whether the general rise of heat represented as 
found on descent into European mines, may not possibly 
admit of a similar explanation." 

Almost simultaneously, a similar conception was put 
forth by Mr. George L. Vose.f "The enormous pressure," 
he says, "generated in the folding of masses of rocks the 
depth of which is measured by miles," must result in 
great mechanical and chemical changes. But Wurtz and 
Vose merely made suggestions. 

Quite independently of Mallet's reasoning and appar- 
ently, also, of the inconspicuous suggestions of Wurtz and 
Vose (though both are mentioned). Professor Joseph Le 

*In a paper read before the American Association at its Buffalo meeting, 
and afterward published in the Amer. Jour, of Mining, Jan. 25, 1868. See 
extract in Amer. Jour. Sci., Ill, v, 385-6. 

tVose: Orographic Geology., or the Origin of Mountains. A Review. Bos- 
ton, 1866. 8vo. 136 pp. 



OROGE]S"IC FORCES. 321 

Conte, of California, arrived at very similar conclusions,* 
and like Mallet presented them with adequate exposition. 
He, however, combined with them Hall's conception of 
copious deposition along a sinking sea-bottom. He went 
beyond Hall, at the same time, in maintaining a local ele- 
vation of the subsided belt, though this was viewed simply 
as the consequence of extensive mashing together, and 
not of folding. "According to my view," he says, " this 
yielding [to tangential thrust] is not by upbending into 
an arch, leaving a hollow space beneath, nor such an arch 
filled and supported by an interior liquid, but a mashing 
or crushing together horizontally^ like dough or plastic 
clay, loith foldings of the strata, and an upswelling and 
thichening of the lohole squeezed mass^^ x\ccording to 
Professor Le Conte's views, previously explained, the 
"upswelling" must be accompanied by a still greater 
downswelling to counterpoise the elevation. This view is 
also maintained by Rev. O. Fisher, who says: "The pecul- 
iar arrangement which is requisite for the equilibrium of 
a disturbed crust resting upon a heavier fluid substratum 
is, that for every subaerial elevation above the mean sur- 
face there must be a corresponding protuberance dipping 
downwards into the fluid below; and, according to the 
relative densities which we have assumed, the depth of 
these protuberances must be about ten times the height of 
the elevations."! The writer proceeds to state that this 
deep protuberance would explain the relative feeble action 
of mountains on the pendulum, since the mountain and its 
"roots" would be less dense than the fluid in which they 

*J. Lc Conte, A TJieory of the Formation of the Great Features of the 
Earth's Surface, Amer. Jour. Sci , III, iv, 345 and 460, Nov. and Dec, 1872. Sup- 
plementary Note, V, 156. Sec T. S. Hunts Criticisms in id., v. 264-70, and Le 
Conte"s Reply in id., v, 448, June, 1873. See J. D. Dana's remarks in id., v, 
26-8. 

t Fisher : Physics of tlie Earth's Crust, 286. Prof. James Hall had previously 
said of mountains, "There is doubtless as much of the mass below the level of 
the sea as above it.'' — Pal. Neto York, iii, Introduction. 
21 



322 A COOLIJs^G PLAXET. 

float; but he states elsewhere that ''the downward protu- 
berances of the crust into the fluid substratum, which we 
have termed the roots of the mountains, will be gradually 
melted," and in this he is unquestionably correct. This 
must cause the mountain gradually to subside to the com- 
mon level, or the elevation must be sustained arch-like, 
with the creation of strains in the contiguous crust. But 
as the mountains have not subsided, they must, therefore, 
consist of elevations without "roots," and these elevated 
masses of matter, so far below the melting temperature, 
must be denser than the underlying fluid. Hence they 
should exert an excess of attraction on the pendulum, 
instead of a deficiency. It seems more probable that the 
elevations are sustained partly by flotation, and partly by 
lateral resistances of the crust, and that the lighter liquid 
fills a portion of the arch, giving the mountain a mean 
density less than if it were completely solid and cold. 

The final crushing together of a geosynclinal, forming 
a mountain protuberance, constitutes what Professor Dana 
has styled a " synclinorium." " In such a process of 
formation," he says, "elevation b}' direct uplift of the 
underlying crust has no necessary place. The attending 
plications may make elevations on a vast scale, and so 
also may the shoves upward along the lines of fracture, 
and crushing may sometim.es add to the effect; but eleva- 
tion from an upward movement of the downward bent 
crust is only an incidental concomitant, if it occur at all."* 

In connection with the effects of crushing pressure, it 
is interesting to recall the older views of Sir Charles 
Lyell: "To assume that any set of strata with which we 
are acquainted are made up of such cohesive and un- 
yielding materials as to be able to resist a power of such 
stupendous energy [as that which uplifted the coast of 
Chili, in 1822 and 1835] if its direction, instead of being 

*Dana, Amer. Journal of Sdence, III, v, 431, 



OROGENIC FORCES. 323 

vertical, happened to be oblique or horizontal, would be 
extremely rasli. But, if they could yield to a sideway 
thrust, even in a slight degree, they would become 
squeezed and folded to any amount, if subjected for a 
sufficient number of times to the repeated action of the 
same force. * * * Among the causes of lateral pres- 
sure, the expansion by heat of large masses of solid stone 
intervening between others which have a different degree 
of expansibility, or which happen not to have their tem- 
perature raised at the same time, may play an important 
l)art. But as we know that rocks have so often sunk down 
thousands of feet below their original level, we can hardly 
doubt that much of the bending of pliant strata, and the 
packing of the same into smaller spaces, have frequently 
been occasioned by subsidence." * 

5. Statement of separate Constructive Conceptions 
relative to Mountain-making, — Having presented a con- 
cise outline of the principal theoretical systems of moun- 
tain-making, we may glance back and eliminate the dis- 
tinct conceptions which have risen into notice from time 
to time, and most of which have some valid grounds for 
recognition, and have contributed something to the final 
theory. They may be enumerated as follows: 

{a) A liquid nucleus and comparatively thin crust. 

Explains internal heat, and instability of earth's surface. 
Objections. Astronomical, based on precession, nutation, tides, 
moon's secular acceleration ; also support of mountain chains. 
[Probably mostly good.] 
{h) A solid nucleus and a plastic zone, either continuous (Fisher) or 
interrupted (W. Hopkins). 
Explains terrestrial rigidity; also, in part, volcanic and seis- 
mic phenomena. 

* Sir C. Lyell : Principles of Geology, 8th ed., 1850, pp. 167-8. The mashing 
process is recognized by Prof. C. H. Hitchcock in his discussion of the White 
Mountains {Geology of Neio Hampshire, i, 518-22, 1874). He also finds strata 
crumpled in detail and not in the mass and all alike, as represented by Rogers 

(icf.jii, 114, 1877). 



324 A COOLIXG PLAXET. 

(c) Action of elastic vapors beneath the crust. 

Explains volcanic and seismic phenomena. 

Objection. Inadequate for mountain formation and mainten- 
ance. [Good.] 
{d) Secular contraction of the earth more rapid in the nucleus, thus 

causing stresses in the crust (C. Prevost). 
(e) The stresses of the crust find relief in wrinkles and plications. 

Explains elevations, anticlinals and synclinals with or without 
plications. 

Objections, (aa) Contraction insufficient (Button, Fisher). [To 
be considered.] (bb) The wrinkles would not serve as germs 
of elongated mountain ranges (Button). [Good.] 
(/) The stresses of the crust find relief in mashing together. 

Explains heat and metamorphism (Wurtz, Mallet) as well as 
plications (Le Conte). 

Objections, {aa) Would not develop sufficient heat (Button). 
[To be considered.] {bb) The heat would not be sufficiently 
localized (Button, Fisher). [Xot good.] 
{g) The mashing together sometimes results in mountain-like up- 
swellings which have still geater down-swellings to counter- 
poise them (Le Conte, Fisher). 

Explains the equilibrium as in an assumed state of flotation, 
and reUeves the crust of strains derived from their weight (if 
that be necessary). 

Objections, {aa) The downward protuberances would be melted 
off. [Good.] {bb) The crust can stand the strain. [Good.] 
[cc) Pendulum phenomena show the mountains deficient in 
mass or density. [Good.] 
(h) A residue of the primitive lieat remains in the earth. 

Explains internal heat and accompanying effects. 
{i) Ascent of isogeothermal planes as a consequence of sedimentation 
(Babbage, Herschel). 

Explains metamorphism of sediments. 

Objection. Boes not explain metamorphism in strata overlying 
strata not metamorphic. [Good.] 
{j) Excessive sedimentation along geosynclinals — these being either 
the effects (Hall) or the cause (Le Conte) of the excess of sedi- 
mentation. 

Explains {ad) deep seated metamorphism ; {hh) great thick- 
ness and fragmental character of mountain formations. 

Objection, Insufficient, as giving no explanation of the longi- 



OROGEKIC FORCES. 325 

tudinal extension of geosynclinals or of the causes which may 
produce them (ocean currents or nuclear contraction). [Good.] 
[k) Igneous and perhaps aqueo-igneous softening along a deep geo- 
synclinal. 

Explains {aa) existence and direction of a line of weakness; 
{hh) Local metamorphisin and vulcanism. 
(?) Contraction under ocean basins developing results more especially 
along continental shores (Dana). 

Explains the border location of mountain chains and volca- 
noes. 

Objection. The ocean bottoms seem to have been also the seat 
of development of contractional results. [Good.] 
{m) Weight of ocean would add something to landward pressure 

resulting from (Z). 
(n) Contractions under extensive plains developing results along 
border chains of mountains. 

Explains {aa) absence of plications from extensive land areas; 
(&&) The border location of mountain chains. 

Objection to {m) and {71). The crust would not slip, even if 
resting on a liquid (Dutton). [Not good.] 
(0) Union of superheated steam with a zone of matter beneath the 
crust, forming a state of igneo-aqueous fusion (Fisher). 

Explains lateral pressure (as the author of it thinks) to sup- 
ply alleged deficiency of contractional tension. 

Objections. Energy insufficient ; action too local and too little 
persistent. [Good.] 
[p] Tidal action on the primitive forming crust, as determinative of 
lines of submeridional structure in the crust. (See this work, 
Part II, Ch. ii, § 6, 4.) 

Explains (aa) existence of elongated geosynclinals ; (bb) Their 
submeridional direction — both otherwise entirely unex- 
plained; [cc) The determination of the oceanic circulation in 
definite submeridional currents, shoidd these be appealed to 
as cause of submeridional sedimentation and subsidence. 
{q) Tidal action on the modern earth as a tributary cause of vulcan- 
ism and seismic phenomena — acting (aa) By the production 
of crushing stresses; (bb) By the partial relief of pressure in 
places, and consequent fusion (King). (See this work. Part 
II, Ch. ii, § 6, 6.) 

Explains relations of these phenomena to lunar and solar posi- 
tions. 



326 A cooli:n^g plaket. 

6. Final Conception of Orogenic History. — This 
series of results, worked out by many minds, probably 
supplies all the principal elements of a final theory. I 
shall, therefore, undertake to furnish the reader with a 
concise digest of orogenic history, framed of those con- 
ceptions which seem best to comport with observed facts, 
and with the operations of ph^^sical forces. 

While the molten earth was growing through the pre- 
cipitation of mineral rains, consolidation began at the 
centre. The heat of the solid nucleus was exceedingly 
intense, and could escape only by conduction to the envel- 
oping fluid, and thence by convection to the terrestrial 
surface. When superficial incrustation began, the fluid 
portion of the earth had fallen nearly to the temperature 
of solidification. The forming crust having a tempera- 
ture little below that of the underl3'ing liquid, its density 
was less, and it floated on the liquid magma; though later, 
when its mean density somewhat exceeded that of the 
magma, its own rigidity may have contributed something 
to its support. At this stage the moon probably was much 
nearer the earth than at present, and the tidal action was 
intense. While in the formative stage, the crust was im- 
pressed by systems of submeridional structure, as a conse- 
quence of the tidal lagging which gave the tidal force of 
the moon an effective tangential component. In this 
action was implanted that bias toward meridionality which 
has revealed itself in all the great primitive features of 
the earth's crust. As a consequence of this, when nuclear 
contraction became operative in the wrinkHng of the crust, 
the wrinkles became elongated and meridional; and the 
contractional results transverse to these produced only 
rugte and knobs in the main wrinkles, or at most, short 
transverse plications. Probably, to some extent also, the 
tendency to latitudinal wrinkling was transformed, over 
plains, by displacement of parts, into movements conform- 



OROGEKIC FORCES. 327 

able with the fundamental and predetermined system of 
wrinkles. This is the only solution of a difficulty which 
Captain Button has shrewdly urged against the contrac- 
tional theory; and the solution seems satisfactory. 

The first ocean spread itself universally over the wrink- 
ling crust. There were ridges and valleys beneath the 
sea. The thickening of the crust experienced an accelera- 
tion. Copious chemical precipitates were thrown down, 
and mechanical detritus was mingled and interstratified 
with the precipitates. The atmosphere had yielded some- 
thing to the gathering sediments, so that the crust re- 
ceived more than it gave. At a later stage the contrac- 
tion of the nucleus enlarged the wrinkles, and the 
inequalities of the sea bottom resulted in partial emer- 
gences. Simple synclinals were now combining into 
geosynclinals. The emergent crust was powerfully eroded, 
and the sediments gathered along the deeper synclinals 
and geosynclinals, more especially if these were located 
near the origin of the sediments. Meanwhile the nuclear 
contraction continued to depress the geosynclinals and 
elevate the geanticlinals. If water, confined beneath the 
crust, was capable of uniting with the molten mass, its 
progressive escape should have supplemented the possibly 
insufficient results of simple nuclear cooling. With acces- 
sion of sedimentary layers to the upper surface of the 
crust, corresponding thicknesses were melted from the 
under surface, except so far as progressive cooling of the 
earth, or diminished conductivity of the crust permitted 
a permanent thickening of the crust. Thus, step by step, 
with the emergence of the geanticlinals, proceeded the 
depression of the geosynclinals, and the filling of certain 
of them with sediments. The excess of sedimentation 
along the geosynclinals caused these regions to experience 
most the melting and softening action of the heat beneath. 
By degrees some of the geosynclinals became composed 



328 A COOLIXG PLACET. 

of softened sediments below, and fresh and imperfectly 
consolidated sediments above, while the main expanses of 
the crust were composed of older and more rigid materials. 
This was especially true of the geanticlinals. The geo- 
synclinals were therefore zones of weakness in the crust. 
With continued nuclear shrinkage, the geosynclinals con- 
tinued to sink and the geanticlinals to rise, until at length 
the lateral thrust of a geanticlinal mass became too great 
for one of the contiguous geosynclinals to bear. The 
geosynclinal refused to be further depressed. The plastic 
mass yielded by collapse. The result was an enormous 
amount of crumpling, plication and crushing of the soft- 
ened strata, with the development of additional heat and 
the formation of faults and slides, and some shoving and 
over-slipping. These effects would be greatest along the 
axis of the geosynclinal. While the geanticlinal subsided 
to some extent, the geosynclinal was levelled up to the sea 
surface, or even hundreds or thousands of feet above it. 
The synclinorium was now complete. There was undoubt- 
edly some, perhaps great, simultaneous downward swelling 
beneath the crumpling geosynclinal, but while the emerged 
protuberance was becoming cold and rigid, the submerged 
protuberance gradually disappeared. Subsequent sub- 
aerial erosions reduced the elevated range to the condition 
in which mountains present themselves to human observa- 
tion, while meantime the wasting material was transported 
into other geosynclinals whose crises had not yet been 
reached. 

It must be confessed that the elevation of the depressed 
geosynclinal into a protuberance of mountain magnitude 
presents some mechanical difficulties which may need to be 
further considered. Is the simple work of crumpling, 
mashing and plication a sufficient explanation of the anti- 
clinal structure, and often enormous elevation, which 
belong to mountain phenomena ? M. Faye has considered 



OROGEKIC FORCES. 329 

the influence of the ocean's bottom temperature upon the 
thickness of the suboceanic crust, and he argues that the 
subsidence of the thickened ocean floor would react be- 
neath the continental areas, and produce all the phenom.ena 
ascribable to upheaval. The doctrine of wrinkling by 
lateral pressure, he dismisses entirely. Now it can be 
readily admitted that such subsidence of ocean bottoms, 
additionally loaded by the weight of ocean waters, would 
result. A part of the subsidence would be compensated 
by refusion on the under surface, as before explained, and 
a residual part would exert a mechanical pressure which 
would react under the land. But the reaction would be 
generally distributed. It might thus tend to upraise broad 
continental surfaces, and force lava through the weak 
places of the crust. But the greater problem in geological 
mechanics is to explain the special and local elevatory 
phenomena seen in mountains, and especially the great 
and numerous folds which have come into existence in the 
principal mountain chains. It is possible that the great 
and constant pressure exerted by the thickened ocean bot- 
toms upon the fluid understratum may determine a constant 
tendency of other parts of the crust to rise, and thus con- 
tribute something to the mechanical agencies which pro- 
duce mountainous elevations on occasion of the collapse of 
a loaded and softened geosynclinal. 

The synclinorium was now more an arch than a geosyn- 
clinal. While, therefore, nucleal contraction continued 
through later ages, the synclinorium presented a form 
which invited further uplifts. It became, in some cases, 
a true geanticlinal undergoing supplementary uplifts from 
age to age, or sometimes sinking as some neighboring 
geosynclinal attained its crisis 

Thus the crests of mountain ranges are lines of fracture, 
and often of prolonged structural weakness. In all cases, 
excessive erosion has thinned and weakened the rocky 



330 A C0OLI]S'G PLAXET. 

covering of the plastic magma which rises into the moun- 
tain form — not, indeed, to a point above the general level 
of the continent, but to a point quite above the general 
level of the under side of the crust — but more especially 
beneath chains of mountains covering elevated regions of 
great breadth, as the Rocky Mountains and the Himalayan 
plateau, * and, as shown to some extent, in the section 
across the Alps, Figure 52. At the same time, the actual 
thickness of the solid material may be greater in moun- 
tains than beneath extensive plains, in consequence of the 
increased amount of radiating surface. Yet, in case of 
reactions of the underlying molten matter against the 
crust, in consequence of local subsidence somewhere, or 
even the general gravitative pressure of the crust, or some 
motion resulting from tidal action, it must be that easiest 
vent, save in case of linear fractures, would be found along 
the crests of mountain ranges. On this reasoning, the 
highest ranges would be most likely to offer easiest relief. 
So volcanic vents should be expected at mountain sum- 
mits as well as along lines of fracture in the level crust. 
At the same time, it is not contended, against the view of 
Mr. Poulett Scrope, that very many — mostly moderate- 
sized — volcanic mountains are not wholly formed from 
erupted matters. 

In this view, the location of a progressing geosynclinal 
and its synclinorian outcome is not determined by the 
ocean. The geosynclinal is an incident of the general 
diversification of the earth's surface contour, and the 
synclinorian outcome depends on the proximity of a source 

*This conceptign is anticipated by Archdeacon Pratt. " It is possible," he 
says, " that the superabundant matter in mountain regions having been heaved 
up from below, or at any rate, having been left aloft as the earth contracted its 
volume, there may be a deficiency of matter below the mountains, which would, 
under certain circumstances, have the tendency of counteracting their effect on 
the plumb line.'" — Pratt : The Figure of the Earth, 4th ed., 87. Compare also 
Airy, Phil. Trans., 1855; Pratt, Phil. Trans., 1858-9, and the results of Schmei- 
zer's observations, in Monthly Notices Ast. Soc, April, 1862. 



OKOGENIC FORCES. 331 

of sediments. Remote from shores, geosynclinals are in 
progress beneath the sea, which will never attain synclin- 
orian crises, unless some revolution provides supplies of 
sediments. The weight of the ocean, nevertheless, must 
have contributed something to the tangential thrust which 
increased the elevation of a synclinorium after it acquired 
the relations of a geanticlinal. This, however, it seems to 
me, must, in some cases, have been exceeded by the tan- 
gential thrust transmitted from a broad continental space 
not undergoing plication, and especially such a space 
already raised into a geanticlinal. The inclination of 
synclinorian folds toward the continent would result rather 
from the continental than from the oceanic thrust. 

Similarly, the border situation of volcanic ranges is 
not due to oceanic action, since the shore-line and the vol- 
canic range have been determined simultaneously by the 
position of a completed synclinorium. The ocean being 
in proximity to the volcano, its water naturally finds access 
to the media destined to be ejected, and even aids in their 
ejection; but it is an error to suppose that elastic vapors 
are capable of doing the greater work of volcanic and 
seismic activity. 

The progress of the geosynclinal would be attended by 
the slow metamorphism of the deep sediments, through 
the agency of internal heat and water. The synclinorian 
crisis would produce plications and elevations, together 
with additional heat and further metamorphism. The 
completion of the synclinorium would be followed by 
completed crystallization and consolidation. Later geanti- 
clinal action would bring the mountain chain to its maxi- 
mum elevation. In still later periods, this elevation would 
be reduced by erosion and by subsidence resulting from 
strains in the contiguous crust, due to the weight of the 
mountain-mass. 

7. Analytical Conspectus of Or o genie Speculations. — 



332 A COOLIXG PLAXET. 

To render as clear as possible to tlie general reader the re- 
lations of the various theories of mountain-making which 
have been passed in review, I introduce here an anah'tical 
exhibit in which the different orogenic conceptions are 
ranged in due order of subordination; and some effort is 
made to annex to the several characteristic conceptions of 
different investigators the views which they have associated 
in their systems with the conceptions contributed by them- 
selves. 

I. Reaction of heated elastic vapors beneath the crust. 

The vapors generated from matter admitted from 
above, 

With a thin terrestrial crust, _ Davy, etc. 

With a solid earth and local lakes of lava, . . _ PIopkixs. 

The vapors generated beneath the crust in a liquid 
or plastic zone, and causing, in fissures, lateral 
compression, crushing and plications, .... Fisher. 

II. Expansion (by heat) of subsided sediments. _ _ _ Babbage. 

III. Depression of thickened crust beneath oceans, and 
reaction on continents, ._.-.--._ Faye. 

IV. Contractional mechanism (C. Prevost, E. de Beau- 
mont, Sedgwick, etc.). 

Meridionality unexplained. 
Fluidity primitive. 

The earth's nucleus fluid (Humboldt, v. Buch, 

etc.), . - . _ _ Old Theory. 

Fluidity or plasticity limited to a zone more or less 
continuous, 
Without intervention of geosynclinals, and with- 
out mashing together. Wrinkling alone. 
Plications the accompaniment of gen- j Kefersteix, 
eral contraction, . _ . _ - "- ( Herschel, etc. 
Plications the result of subsidence of fold; 
thickened strata resulting from erosion of 
granitic nucleus of mountain, .... Whitney. 
With the intervention of geosynclinals (Hall). 
Subsidence caused by weiglit of sediments (Hall), 
and deep-seated condensation (Hunt): moun- 
tains onlv relief features of eroded conti- 



OROGENIC FORCES. 333 

nents, in earlier times somehow elevated 
(Buffon, de Montlosier, Lesley); subsidence 
resulting in motion or fermentation and 
pressure, which, with moderate accession of 
heat from below, cause metamorphism, etc., 
(Hall) [Continental elevation not explained]. 
Subsidence the principal cause of the corru- 
gations of the earth's strata, .... Hall. 
Subsidence not the principal cause of the 
earth's corrugations, but only of their po- 
sition and direction. A zone of plastic 
material in aqiieo-igneous fusion beneath 
the crust, augmented by subsidence caus- 
ing vulcanic phenomena and softening of 
deep crust, forming lines of weakness 
along which are developed results of con- 
traction of the earth and of the deep 

crust itself, Hunt. 

Subsidence caused progressively by lithifica- 
tion below, and increasing density, and after- 
ward aqueo-igneous fusion, metamorphism 
and slaty cleavage, and determination of line 
of weakness and yielding to horizontal pres- 
sure; no elevation except by crushing to- 
gether, with iipswelling and corresponding 
down swelling Heat partly primitive, 
partly of chemical origin. Continents and 
ocean basins resulting from unequal radial 
contraction. [No explanation of elevation 

without plications.] ._ Le Coxte. 

Subsidence an incident of general contraction. 
Copious sedimentation along geosynclinals. 
Finally, plications, shoving along fractures, 
and some crushing, resulting in elevation. 
Geanticlinal elevations discriminated. In- 
creased pressure from the side of the great 

oceans, __.__ _ Dana. 

Fluidity not necessarily primitive (Wurtz, Mallet). 
Fluidity caused by contractional evolution of heat. 

Heat resulting from pressure and chemical action. Vose. 
Heat resulting from crushing of earth's crust. 



334 A COOLING PLAXET. 

with accompanying thermal and mechanical 
consequences, and variations in rate of in- 
crease of hypogeal temperature. .... Mallf.t. 
Meridionality of crust-structures due to primitive tidal 
action. Fluidity contractional, tidal, and perhaps 
primitive. Sedimentation along geosynelinals located 
in position and direction by the lunar tidal actions on 
the primitive earth ; mashing together with plications 
and metamorphism ; consequent elevation and cor- 
responding depression; the depression progressively 
removed by re-fusion, and the mountain standing- 
somewhat arch-like, with a molten or highly heated 
core and lower density; weight of mountain pro- 
ducing strains in the crust, mountain consequently 
undergoing secular subsidence. Geanticlinal eleva- 
tions produced by lateral pressure resulting from 
contraction, and secondarily, in part, from weight 
of mountains. Submarine geosynelinals and gean- 
ticlinals as well as continental, and hence no greater 
contractional pressure from oceanic side, . . . This Work. 

Various other suggestions have been made during the 
history of geological speculation, most of which have 
never gained any particular repute. M. de Boucheporn 
conjectured that each geological revolution was the result 
of a sudden change in the direction of the earth's axis, 
caused by collision with a comet. The shock before the 
last, for instance, left the ec^uator in the position of the 
Andes chain; the last left it in the actual position; the 
next will produce still another revolution. Geologists 
have also considered the possibility of a change in the axis 
resulting from a redistribution of the land and Avater — 
but this more especially to explain vicissitudes of climate.* 

* Sir Wm. Thomson, Bnt. Assoc. Bep., 18T6, Part II, p. 11 : Trans. Geol. Soc, 
Glasgow, iv, 3i:i; Haughtoii, Proc. Boy. Soc, xxvi, 51, April 4, 1878; Nature, 
xviii, 266-8; G. H. Darwin, Trans. Roy. Soc, clxvii. Part I: I. F. Twisden, 
Qaar. Jour. Geol. Soc, Feb., 18T8: Airy, Aihenoeum, 22 Sep.. 1869: Croll, Geol. 
Mag., Sep.. 1878; E. Hill, Geol. Mag., June, 1878. See also Laplace: Systeme du 
Monde, ed. 1824, p :B9"2. For some recent views on the tendency of the earth's 
crust to subside under pressure, see J. Starkie Gardner, in Nature, xxviii, 323-7, 
August 2, 1883. 



THE PLAKETAKY CRUST. 335 

This speculation, however, generally leaves the cause of 
tlie change, even if real, unaccounted for. Rev. O. Fisher 
suggested, on the strength of Darwin's theory of the 
separation of the moon from the plastic earth, that perhaps 
the ocean basin represents the cavity left on that occasion.* 

§ 11. UNEQUAL THICKNESS OF THE PLANETARY CRUST. 

Let us recur for a moment to tlie physical conditions 
coexisting with the mountain masses whose origin w^e have 
souglit to discover. AYith tlie progressive development of 
wrinkles, groups of wrinkles and continental expanses, a 
gradual differentiation of different regions of the planetary 
surface would be in progress. This would produce that 
diversification of conditions which would be attended by 
an ever-increasing diversification in the organic aspects of 
land and water — since, as will be remembered, this dis- 
cussion concerns for the present a planet upon which water 
has existence. As we can hardly suppose conditions on 
such a planet, under which no molecular disintegration 
would take place, we must conclude that the emerged and 
uplifted folds and synclinorian arches of the crust would 
be exposed to perpetual denudation; and this would ulti- 
mately thin the crust along the axes of the great folds and 
arches to such an extent that the mountains of anticlinal 
structure would tend to become mere shells filled with 
molten matter, or at least matter of a very high tempera- 
ture. This condition of mountain masses would of course 
impart to them a density less than that of the average 
crust beneath the plains. As another result, the mountain 
crests would be lines of great relative weakness; and 
hence any pressure acting from beneath would be most 
likely to find relief through mountain summits. At the 
same time, the heated matter within and beneath the 

* O. Fisher, Jsfature^ xxv, 243-4. 



336 A COOLIXG PLAXET. 

mountain would be exposed to a freer radiation than the 
matter beneath the plain, and for this reason the solid crust 
should be able to thicken with a pace somewhat equal to 
the wastage by denudation. But if tidal movements of 
the crust, or currents or tidal swells in the subjacent liquid 
should create a predisposition in the molten matter to seek 
and frequent the spaces under the mountain anticlinals, 
this cause might interfere with the thickening due to the 
unusual exposure of a mountain convexity to the process 
of radiation, and thus preserve the unusual thinness which 
tends to result from surface erosions. 

Now, tidal influences would tend to cause currents in 
the molten interior. As soon as the crust shall come to 
possess any sensible rigidity, the height to which the tidal 
swell would rise would be somewhat less than that wdiich 
the same attraction would produce in a fluid. The under- 
lying fluid would, therefore, press against the under side of 
the tidal arch. If at such a time, a vent should exist or 
be opened in the arch, the fluid would escape, and this 
would determine currents toward the place of outlet. Such 
vents would be most likely to be opened when the crest of 
the tidal swell should coincide with the line of weakness 
along a mountain anticlinal. The result would be an influx 
of molten matter from all directions; and the effect of this 
would be to prevent thickening of the mountain fold, if it 
did not actually reduce its thickness. Further tlian this, 
the very existence of permanent swells or folds in the 
crust would be the condition of translatory movements in 
the underh'ing liquid. The partial rigidity of the crust, 
as just stated, would cause the underlying liquid to press 
against it. This pressure would be transferred westward 
from point to point. There would be a time when the 
apex of the tidal swell would be near the base of an anti- 
clinal fold. It is, therefore, obvious that the pressure in 
this situation would initiate an actual motion of the fluid 



THE PLANETARY CRUST. 337 

in the direction of relief — that is, toward the crest of the 
anticlinal. It is quite true that the tidal pressure would 
reach and pass the anticlinal before the relief which the 
latter would afford could be fully realized. But the fluid 
w^ould have received an impulse toward the anticlinal 
which would live for some time after the tide had passed. 
This impulse would be renewed at every semi-rotation of 
the planet perpetually. I imagine that the consequence 
would be the perpetual transference of more highly heated 
matter to the region under the fold, and the prevention of 
normal increase of thickness. 

On the contrary, some causes may exist for a greater 
than average thickness under masses of ocean waters. In 
the first place, the continual accumulation of sediments 
would not be fully offset by fusion upon the under side of 
the crust; nor even to such extent as the secular cooling 
of the planet and thickening of the crust would imply. 
The accumulation takes the initiative, and the removal 
from below is the reaction. The time which separates the 
action and the reaction would give opportunity for some 
uncompensated accumulation. But, in the second place, 
the normal circulation of oceanic waters would keep a 
stratum of nearly ice-cold water upon the bottom, spread 
over the ocean's floor. This is a colder temperature than 
the mean temperature of the atmosphere in any except 
subarctic and arctic regions. The planetary crust, there- 
fore, is exposed to a more effective cooling temperature 
under the oceans than on the land. Finally, the water in 
contact with the crust under the oceans is a better conduc- 
tor of heat than the atmosphere in contact with the land. 
These three reasons would conspire to produce a thicker 
crust under the oceans than under the continental surfaces. 
32 



CHAPTEE III. 

SPECIAL PLANETOLOGY, 

OR PEESEXT CONDITION AXD COSMOGONIC HISTORY OF 
THE PLAXETAEY BODIES OF OUR SYSTEM. 

§ 1. THE EARTH. 

Each orb has had its history. For ours, 

It blazed and steamed, cooled and contracted, till, 

Tired of mere vaporing within the grasp 

Of ruthless condensation, it assumed 

Its present form, proportions, magnitude — 

Our tidy ball, axled eight thousand miles.— Daa'id Masson. 

ACC0RDI2sG to nebular theory, all the members of 
-^^^ our system must pass sooner or later, through the 
same succession of stages. The circumstances of different 
planetary bodies, however, have differed widely, and the 
details of their evolution have assumed very diversified 
aspects. The principal factors concerned in the special 
histories of these bodies, so far as we can judge, are mass, 
volume, distance from the sun, age, and magnitude of the 
tidal actions exerted upon them. Connected with mass 
and volume are the quantity of atmosphere and its density 
on the planetary surface, and hence the temperature of 
steam formation and the thermal effect of solar radiation. 
Let us consider attentively the probable influences of the 
diversified conditions of planetary existence in our system, 
beginning with those bodies most accessible to physical 
inquiry. 

Our planetary home occupies the temperate zone of the 
solar system. It presents us also an array of facts from 
which we may verify many of the conclusions deductively 



THE EARTH. 339 

reached from physical principles. We have here innu- 
merable surface indications of a former high temperature 
upon the exterior of the globe. Numerous other phenomena 
testify to the perpetuation or perpetual production of a high 
temperature at all considerable depths beneath the sur- 
face. The records of extinct life testify to a progressive 
subsidence of temperature during long past ages, and pos- 
sibly also, to a diminution of solar heat; and wide-spread 
sheets of marine sediments declare the former existence of 
a universal ocean. 

1. Condition of the Marthas Interior, — That great 
heat exists within the earth is abundantly demonstrated; 
but the condition of the general interior has been much 
discussed. Sir Humphrey Davy,* Daubeneyf and others 
maintained that chemical action was adequate to produce 
the thermal, dislocating and orographic phenomena 
which have been observed. Mr. F. M. Endlich has re- 
cently detailed remarkable thermal and explosive mani- 
festations on the island of Dominica, which he thinks 
clearly attributable to chemical action, but which so much 
resemble volcanic action as to give good countenance to 
Davy's theory. J; 

An opinion for a long time more widely accepted, was 
that which conceived the great interior mass of the earth 
as existing in a molten state, and the solid portion as con- 
stituting a mere film commonly designated the crust. This 
conception has coffie down from Descartes § and Leibnitz, || 
and until recently, has been very widely accepted. 

* Davy, Phil. Trans., 18-28, 1832. 

tDaubeney, Jameson's Edinb. New Phil. Jour., liii, and Eacyc. Met.., pt. 40. 
See also Eniii? : 07'igm of (he S/a}s, and Studcr : Geologic der Schweiz. 

t Endlich, Tlie American Naturalist, xiv, 761-72, November, 1880. 

§ Descartes: Princijyes dela Philosophie, 1044, pt. iv, §§ 2, 44, 72. 

i Leibnitz: Acta Eruditornm, Jannary, 169:3, and Protoga;a, 1749. Compare 
also Newton: Principia Mathem^atica Philosoj)hice Naturalis, 1667, and Buffon: 
Epoques de la Nature, 1778. For statement of Leibnitz' speculations, see Part 
IV, §4. 



340 SPECIAL PLAXETOLOCtY. 

The whole doctrine of a molten interior was objected 
to by Professor W. Hopkins* on the ground that the 
phenomena of precession and nutation could not be what 
they are unless the earth were solid, or had, at least, a 
crust from 800 to 1,000 miles in thickness — sufficiently 
thick to give it a high degree of rigidity. The idea was 
taken up from new considerations and reinforced by Sir 
William Thomson in several remarkable scientific me- 
moirs,! in which he distinctly maintained the theory of a 
solid globe; though he claimed that the solidity of the 
central portion may be the result of pressure of the super- 
incumbent portions. Geologists and physicists generally 
have shown a disposition to acquiesce in the judgment of 
such mathematicians. It does not appear, however, to 
the writer that the astronomical considerations are con- 
clusive, since whatever external attractions are exerted on 
the protuberant crust about the equator would be almost 
equally felt by the protuberant magma underneath the 
crust, and the solid and liquid portions of the equatorial 
protuberance would tend to move consentaneously. It is 
quite true that the crust-protuberance would be slightly 
more affected than the molten protuberance beneath it, 
both because it would be slightly nearer the attracting 
body, and because the eccentricity of successively interior 
zones may be regarded as successively less. Still, if the 
thickness of the crust is held to be but a few miles, these 
differences must be almost too slight t# enter into calcula- 
tion, and would be mostly concealed by the presumable 
viscosity of the molten magma, and the friction upon 
itself and the enveloping crust. The defects in the argu- 

* Trans. Roy. Soc, 1836, p. 382: 1838, p. 38: 1840, p. 193: 1&42. p. 48. His 
three memoirs for iaS9, 1840 and 1842 embrace a complete investigation of the 
snbject. See, also. On the Geological Theories of Elevofion and Earthquakes in 
Brit. Assoc. Rep., 1847, pp. 3:3-93; also Quar.Joiir. Geol. Soc, viii, 56. 

tSir W. Thomson, Trans. Roy. Soc, May, 1862; Thomson and Tait: Nat. 
Philosophy^ vol. i. 



THE EARTH. 341 

ment for Internal solidity, based on the phenomena of 
precession and nutation, were pointed out by Delaunay,* 
who maintained that the motions of precession and nuta- 
tion are so slow that the internal fluid, in consequence of 
friction and viscosity, would partake precisely of the mo- 
tion of the crust. Archdeacon Pratt, however, dissents 
from Delaunay,! while General Barnard holds that Hop- 
kins' results are vitiated by an oversight. | The problem 
has also been discussed by Hennessey and Haughton.§ 
Sir William Thomson informs us also that Professor New- 
comb does not admit the validity of the reasoning from 
precession and nutation,] and that Newcomb's doubts led 
him to a reinvestigation of the problem, the result of 
which was a confirmation of the doctrine of internal solid- 
ity, with some qualifications in the actual case. In a still 
later utterance, however, Sir William Thomson admits 
that ''the arguments derived from the phenomena of pre- 
cession and nutation present considerable difficulties, and, 
indeed, do not afford us, at the present time, a decisive 
answer.^ In reference to this particular argument for 
internal solidity we may, therefore, unite with Rev. O. 
Fisher in pronouncing it obsolete. ^"^ 

This, however, is not to abandon the theory of internal 
solidity. There still remains a body of considerations 
lying in the border ground between terrestrial and cosmi- 
cal physics, which furnish evidence not yet invalidated, 

* Comxites Bendus, 1868; translated in Geological Magazine, v, 507, Nov., 
1868. Also Cours EUmentaire d'' Astronomie, 643, 644. 

+ Pratt r Figure of the Earth, 4th ed., 133-6. 

i Barnard, Problems of Rotary Motion, Smithgonian Contrib., No. 240, 
New Addendum, p. 42, vol. xix, 1871. 

§ Hennessey. P/«L Trans., 1851,545; Trans. Roy. Irish Acad., 1852; Phil. 
Mag., Sept., 1860. 

II Sir W. Thomson, Glasgoiu Address, Brit. Assoc, 1876, Amer. Jour. Sci., 
Ill, xii, 342. 

1[ Sir W. Thomson, Trans. Geol. Soc, Glasgow, 1879, p. 48. 

**Rev. O. Fisher: Physics of the Earth's Crust, London, 1881, p. 22. This is 
a very important work. 



342 SPECIAL PLAXETOLOGY. 

that the earth must possess a high degree of rigidity. These 
considerations are supplied by the phenomena and the 
philosophy of tides; and have been likewise profoundly 
discussed by Sir William Thomson * and Archdeacon 
Pratt.f Were the terrestrial crust so jdelding as to offer 
only fluid resistance to tidal action, it would rise and sink 
with the waters of the sea, so that the ocean tides would 
produce no increase or diminution of depth4 If, on the 
contrary, the earth were perfectly rigid, the whole tidal 
action would be developed in the waters, and the tides 
would increase the depth to a certain extent. The amount 
of this increase of depth has been calculated, but tidal ob- 
servations have not yet been sufficiently exact to deter- 
mine how the facts correspond with the theory of a 
perfectly rigid globe. The actual tide, however, seems to 
be somewhat less than the theoretical tide, and this affords 
some inductive ground for the theory that while the earth 
possesses a high degree of rigidity it is not perfectly 
rigid. Perfect rigidity would not, indeed, exist even in a 
globe of steel. Sir William Thomson has shown that if 
the earth were as rigid as steel the amount of its yielding 
to tidal action would be such that the ocean tides would 
be only two-thirds of what the\^ would be with perfect 
terrestrial rigidity ;§ if the earth were no more rigid than 
glass, the relative rise of the ocean tide would give a 
depth only two-fifths || of that on a perfectly rigid globe. 
Now the theoretical height of the tides has been calcu- 
lated on the assumption of perfect terrestrial rigidity; and 
it is incredible that the actual tides should be only two- 
thirds of the requirement of theory without a discovery 

* Sir W. Thomson, Phil. Trans.. 1863, p. 574; Trans. Geol. Soc, Glasgow, vi, 
48-9. 

t Pratt: Figure of the Earth. 4th ed., 138-40. 

tSee explanations, Pt. II, chap, ii, § 6, 1. 

§ Archdeacon Pratt brings out the result "three-fifths." 

II According to Pratt, " two-ninths."' 



THE EARTH. 343 

of the discrepancy by means of observation. The whole 
earth must, therefore, be more rigid than glass. Such a 
degree of rigidity could not be imparted by a rocky crust 
having a thickness of fifty or a hundred or five hundred 
miles. Such rigidity may well be conceived to result 
from the general solidification of the interior. This, how- 
ever, as before explained, would not result from the laW' 
which correlates solidifying point with amount of pressure 
sustained. 

Mr. G. H. Darwin, in the course of his researches on 
the cosmic influence of tides, has incidentally arrived at 
confirmations of the doctrine of internal rigidity. He 
has shown that the diurnal and semi-diurnal bodily or 
deformative tides produced in the earth by the moon are 
not sufficient to reveal their existence in the secular accel- 
eration of the moon's mean motion, though Sir William 
Thomson had assumed the two phenomena reciprocally 
connected.* The support of mountain masses implies also 
a high degree of rigidity. Mr. Darwin has shown that 
either the materials of the earth have about the strength 
of granite, at 1,000 miles from the surface, or they have a 
much greater strength nearer the surface. f 

Still more recently Mr. (now Professor) G. H. Darwin 
has subjected the rigidity of the earth to a new discus- 
sion. | Abandoning the study of diurnal and semi-diurnal 
tides as too much influenced by meteorological accidents, 
he fixes on the lunar fortnightly declinational tide, and 
the lunar monthly elliptic tide. Using for data the Tidal 
Reports of the British Association, and the Indian Tide 
Tables, for a period of thirty-three years, at fourteen dif- 
ferent ports in England, France and India, and taking due 
account of the interferences of the land masses of the 

♦G. H. Darwin, Proc. Brit. Assoc, Dublin, 1878, Nature, xviii, 581. 
tG. H. Darwin, Proc. Roy. Soc, June 16, 1881. 

J Paper read at the British Association, Southampton meeting, 1882. Pub- 
lished in Nature,xxYii, 22-3, Nov. 2, 1882. 



344 SPECIAL PLAXETOLOf^Y. 

earth, he finds, after a most laborious calculation, that, 
taking- all the observations together, there "seems to be 
some evidence of a tidal yielding of the earth's mass," 
but that "the effective rigidity of the whole earth is about 
equal to that of steel." If only the Indian observations 
are used for a period of forty-eight years, the rigidity 
appears to be somewhat greater. "On the whole, we may 
fairly conclude," he says, "that, while there is some evi- 
dence of a tidal yielding of the earth's mass, that yielding 
is certainly small, and the effective rigidity is at least as 
great as steel." * 

Admitting the general solidity of the earth, it is still 
evident that large supplies of molten matter exist within. 
Now we may rationally conceive three independent causes 
of a state of liquefaction at some depth beneath the 
surface. 

(1.) There may be a zone too deep for solidification by 
cooling and too shallow for solidification by pressure. Or, 
in more exact terms, the downward increase of terrestrial 
temperature for a certain distance may be more rapid than 
the rise of that function of pressure Avhich produces 
solidification; but at greater distances from the surface, 
less rapid than the rise of the same function. During the 
first interval the pressure will not be sufficient to produce 
solidification at the temperature existing; but during the 
deeper descent the pressure will be enough or more than 
enough to produce solidification at all temperatures at- 
tained. 

It appears probable that the earth's internal tempera- 

* The use of all the data gives 

a;=.676 ± .076, y=.029 ± .065. 
where the approximation to complete rigidity is expressed by the approximation 
of the value of x to unity : and the value of ij approaches zero as the amount of 
fluid frictiou diminishes. The numbers given with alternative signs are the 
probable errors. The use of only the Indian data gives 

X=.931 ± .056. y=.155 ± .068. 



THE EARTH. 345 

ture does not continue to increase downward in uniform 
ratio with the depth, but that the rate of increase dimin- 
ishes. As to the internal pressure, it must increase at a 
rate greater than the increase of depth; since it is demon- 
strated that the density of terrestrial matter increases 
toward the centre. The mean density of rocks at the 
surface is about 2.65, while the mean density of the whole 
earth is about 5.5. The density of the centre is made 
10.74 by Pratt, who takes surface density at 2.75; and 
9.59, by Waltershausen, who takes surface density at 
2.66. The law of increase of density is unknown, but 
Waltershausen has assumed a formula* which gives the 
density inversely as the square of the distance from the 
centre; and Archdeacon Pratt has adopted and independ- 
ently established the formula of Laplace, which makes 
the increase of the density vary as the square root of the 
increase of pressure. Each successive layer of uniform 
thickness must add, therefore, an increasingly greater 
amount to the pressure exerted upon the parts within, 
and also to their density, unless we assume that the com- 
pressibility of terrestrial matter exists only within certain 
limits of pressure. 

(2.) In the next place we may suppose that at all 
depths beneath the surface the pressure is such that the 
fusing point is higher than the actual temperature, so that 
a state of solidity exists. If, now, the pressure within 
any region becomes diminished to a certain extent^ the 
fusing point may be lowered to the actual temperature, 
where a state of fusion will supervene. Now, we may 
conceive the pressure to be diminished by the opening of 
a fissure from the surface. In this case, all the matter 
relieved may dissolve into a state of fusion, and this first 

* Waltershausen: Rocks of Sicily and Iceland, p. 315. His formula is 
P'=P-(P — P)r2 
where p' is the density at the distance r from the centre, p is the surface density 
and P the density at the centre. 



346 SPECIAL PLAKETOLOGY. 

fused matter may be crowded upward through the fissure 
by the pressure of contiguous matter, which, in turn, as 
soon as relieved, will be fused and ejected through ihe 
fissure in a similar way. Thus, it may be conceived, a 
copious fissure outflow of melted matter might be occa- 
sioned. Or, we may conceive the relief from pressure to 
result, as Professor William Hopkins suggested, by the 
partial support of an overlying arch bulged up by lateral 
pressure. Or, finally, we may look to the removal of vast 
overlying formations by surface erosion, as the source of 
such diminution of deep pressure as would lower the 
fusing temperature to the actual temperature. Mr. Clar- 
ence King has considered this cause attentively, and has 
enunciated the opinion that it answers the requirements 
of the case.* He has remarked that periods of copious 
volcanic overflow have followed periods of extensive ero- 
sion of mountains and plateaus, and that the succession in 
the nature of the erupted materials at different localities 
and different epochs is such as is best explained by the 
supposition of isolated lakes of molten matter, such as 
would arise from local and somewhat sudden diminution 
of pressure. t 

(3.) We may conceive that heat and fusion result from 
some mechanical crushing pressure. With Mallet and 
others we may conclude that local fusion is produced 
through the crushing effects of enormous lateral pressure 
resulting from the secular contraction of the earth in its 
slow process of cooling. Mr. Mallet advocated this view 

* King: Geolog. Exploration kOth Parallel, i. p. 706, seq. 

t In the foregoing paragraph I have employed the usual language, but, as 
before explained (p. 270), I do not consider it exact, since the solidification which 
exists at great depths and at a high temperature, is not analogous with normal 
crystalline freezing, but is merely a consolidation by confinement of molecules 
in fixed positions. Pressure lowers the normal freezing point of molten rocks 
Instead of raising it. But the principle stated is valid under either view. 



THE EARTH. 34? 

with great ability and great persistence.* But it has been 
opposed as inadequate by numerous competent writers, f 
By some it has been shown that the total contraction of 
the earth is insufficient, and by others, that the effects are 
so much diffused as not to attain a condition of disturb- 
ance at distinct localities. It may fairly be claimed, never- 
theless, that the effects of contraction would be diffused 
only in proportion as all the physical conditions of the 
earth's crust are everywhere uniform; while such uniform- 
ity is contradicted by all our familiar observations on the 
crust. So far as secular contraction gives rise, therefore, 
to lateral pressure, we must expect the crushing, and 
therefore the heating effects, to be accumulated in the 
weakest regions of the crust. 

But a cause of crushing pressure which seems to me 
more adequate than secular cooling is suggested by Sir 
William Thomson's and Archdeacon Pratt's and, we may 
add, Professor G. H. Darwin's, demonstrations of tidal 
effects in a globe as rigid as steel or glass. May not 
the tidal deformations of the earth's crust be the source 
of the internal heat which manifests itself in fluidity? The 
whole value of the lunar tidal oscillation in a yielding 
globe should be about 58 inches. In a globe as rigid as 
glass it should therefore be about 34.8 inches, and in one 
as rigid as steel, 19.33 inches. The whole tidal oscillation 
under the joint maximum influence of the sun and moon 
in a perfectly yielding globe would be, about 81.2 inches. 

* Besides a long series of memoirs on the theory and phenomena of volca- 
noes and earthquakes, cited in the author's Syllabus, p. 73, the reader may con- 
sult, especially, Mallet, On the Temperature Aftainahle by Rock-crushing, and 
its Consequences, Phil. Mag., July 1875, 1-13. and Amer. Jour. Sci., Ill, x, 256-68, 
and xii, 463; also Phil. Mag., v, i, 19-22. 

tSir W. Thomson, Nature, Jan. 18 and Feb. 1, 1872; O. Fisher, Quar. ,Jour. 
Gwl. Soc, Lond., xxxi, 469-72, May 12, 1875; Phil. Mag., iv, 1, 302-19, Oct., 1875; 
id., V, i. 38-42; Physics of the Earth's Crust, ch. iv, v, vi. Criticisms are made 
also by Gen. G. J. Barnard, Smithsonian Contributions, No. 240, and by E. W. 
Hilgard, Amer. Jour. Sci., Ill, vii, 535-46, June, 1874, and Phil. Mag., July, 1874, 
41. 



348 SPECIAL PLAKETOLOGY. 

The amount in a globe of glass would therefore be, when 
at a maximum, 48.72 inches and in a globe of steel, 27. OG 
inches. Should the terrestrial globe yield to the extent 
of any one of these amounts, the crushing effect expe- 
rienced by the superior zones of the crust would not be 
uniformly distributed, since variations in structure and 
hardness and surface configuration would preserve certain 
portions Jfrom any change, and the whole amount of the 
interstitial displacements would be accumulated in the 
remaining portions. It does not seem at all improbable 
that the transformation of such enormous mechanical force 
into heat should suffice to bring to a state of fusion vol- 
umes considerable enough to answer all the requirements 
of the thermal manifestations of modern times, as well as 
the terrestrial movements of modern earthquakes. 

The extended series of observations on earthquake phe- 
nomena collected by the late M. Alexis Perrey and by the 
British Association, are generally thought to indicate a 
real connection between such phenomena and the positions 
of the sun and moon. Thus (a) earthquake shocks are 
more frequent at the time of lunar syzygies than at the 
quadratures.* As the tidal effects of the moon and sun 
are as 5 to 2, their conspiring effects at the syzygies are 
as 7 and their conflicting effects at quadratures are as 3. 
If the seismic consequences of a range from 7 to 3 are 
observable as a differential — that is, if a tidal influence 
represented by 4 is a reality, then still more must a tidal 
influence represented by 5 or 7 be a reality. 

[b) Seismic phenomena are more frequent when the 
moon is in perigee than when in apogee, f The difference 
between the maximum and minimum distances of the 
moon from the earth is about 31,355 miles. The tide-pro- 

* A. Perrey, cited in Amer. Jour. Sci., II, xxxvii, 1; III, xi, 233; Pop. Sci. 
Monthly^ xvii, 457. 

■^Pop. Sci,. Monthly, xvii, 458. 



THE EARTH. 349 

ducing efficiency of an attracting body is inversely as the 
cube of the distance. The lunar tide in perigee will there- 
fore be to the lunar tide in apogee as 1.487 to unity. 
Here is a variation amounting to 49 per cent of the apogee 
tidal efficiency. A variation of 49 per cent of the mini- 
mum tide-producing efficiency is, it thus appears, the 
cause of a certain observed variation in earthquake action. 
The whole lunar force, therefore, may be the cause of 
the regular body of seismic phenomena. 

(c) Earthquakes are more frequent with the moon in 
the meridian than with the moon in the horizon. In the 
former case, the lunar tide is at flood or nearly so, and in 
the latter, nearly at ebb. This result confirms the conclu- 
sion that lunar attractions cause relative movements in 
different parts of the terrestrial crust, and show that the 
elevatory effects are more disturbing than the ebb-tide 
subsidences. When the crust over two opposite quarters 
of the earth's surface subsides simultaneously with corre- 
sponding elevations over the two intervening quarters, it 
perhaps results that the subsiding quadrants are more uni- 
formly and more firmly braced than the rising quadrants, 
and would therefore experience less local motion than 
they. 

The observational determination and measurement of 
the geological tide-wave is a subject of extreme delicacy. 
Were all the disturbing influences acting on the oceanic 
waves suspended for a period, observation would readily 
determine the actual fluctuation caused by lunar and solar 
attractions, and the difference between these and the fluc- 
tuations deducible on the theory of a perfectly rigid globe 
would reveal the extent which the earth falls short of per- 
fect rigidity. It is probable that tidal observations, made 
under the direction of the highest science, will ultimately 
eliminate disturbing effects arising from winds, barometric 
Dressure and other causes, and make known the actual ex- 



350 SPECIAL PLAi^ETOLOGY. 

tent of tidal fluctuations in the open sea. Sir William 
Thomson has pointed out some conceivable experiments 
which would result in the very desirable solution of this 
problem. He supposes a water pipe twelve kilometers in 
length, submerged to protect it from variations in atmos- 
pheric pressure, and turned up at each end into the free 
atmosphere. Then, if the earth were perfectly rigid, and 
the pressure of the air equal at the two extremities, the 
water would rise in the more southern end during the pas- 
sage of the moon over the meridian. Or, if a plumb line 
were susjoended from a great height, and could be kept 
perfectly free from atmospheric disturbance, it would be 
deflected always toward the nearest tidal swell, except 
that when the moon were in the horizon or in the meridian, 
the attractions from opposite directions would neutralize 
each other. The greatest deflection would always be at 
the distance of 45° north or south of the position corre- 
sponding to the moon's declination, and the greatest deflec- 
tion for any particular locality would be when the moon is 
45° above or below the horizon. The greatest deflection 
of the line, however, would be only one twelve-millionth 
of its length, and this movement could hardly be made 
perceptible in a line of any practicable length. 

2. Siihmeridional Trends hi the Earth^s Prhnitive 
Structure. — As important tidal influences must always 
have existed on the earth's surface, we may continue to 
discover in the oldest records of the earth's solidifying 
state, some traces of tidal action. I am inclined to think 
we discover such in the prevailing meridional trends of the 
oldest mountain ranges. I have stated that the trans- 
meridional progress of the tidal swell in early incrustive 
times on any planet, must give the forming crust structural 
characteristics and aptitudes trending from north to south. 
I have stated also that the horizontal component of the 
tidal action on a lagging tidal swell would tend to give 



THE EAKTH. 351 

the swell an actual motion of translation toward the west. 
Suppose the tide-wave to lag an hour behind the moon's 
meridian passage, it can readily be shown that the horizon- 
tal component of the moon's attraction upon the wave is 
one two hundred and twenty-sixth of the whole tide-pro- 
ducing effort of the moon.* Such a motive to actual 
translatory motion is by no means inconsiderable — the 
less so when we reflect that it is not directly opposed by 
gravity, as in the case of the tidal elevation, but only by 
the friction and inertia of the water. 

When, therefore, the earliest wrinkles came into exist- 
ence their axes would be meridional or submeridional. 
Now, some of the oldest beginnings of mountain devel- 
opment upon the earth are seen in the submeridional 
Laurentian ridges; in some of the Appalachian ranges, as 
the Blue Ridge, the Highlands of New York and Black 
Mountain of North Carolina; in some ranges of the Rocky 
Mountains, as Colorado, Medicine Bow and Park Ranges, 
in the Humboldt Range, and in the whole system of the 
so-called "Basi*i Ranges." Not materially later are the 
Green Mountains, the White Mountain system, the other 
principal orographic foundations of the Rocky Mountain, 
Sierra Nevada and Cascade chains, all equally meridional. 
In Europe, the Scandinavian range, the Urals, the Cam- 
brian Mountains, the East Adriatic Alps; in Asia, the 
Yablonoi, the ranges of Indo China, the Malayan penin- 
sula and islands, and those of Japan, Kamtchatka and 
northeastern China; in Africa, the entire east and west 
coast ranges, and those of Madagascar, all conform approx- 
imately to the direction of the meridian. It is also proba- 

* If in the formula previously given (p. 233) we assume in the case of the 
moon and earth, a=15°, T 0=3959 andE T=240,000, then T A^Fx^lM^TrX tan 
15° = . 00442 F=^|^^ F nearly, where F represents the moon's attraction at the 
earth's surface and T A represents roughly its horizontal component at the dis- 
tance of 15° from the zenith point. 



352 SPECIAL PLAXETOLOGY. 

ble that the foundations were early laid for the Sierra 
Madre Mountains in Mexico, and the Andes and the Serro 
Espinaco and Organ Mountains of South America. The 
crests of these mountain ranges may probably be regarded 
as ancient co-tidal lines, and these mountains are, to some 
extent, frozen billows, in the solidifying terrestrial surface, 
thrust, indeed, far above their original altitudes by the 
lateral pressure to which the shrinkage of the earth's 
interior has subjected them. 

More than this, the whole general expression of the 
earth's surface configuration should preserve traces of the 
same primitive tidal action. (1) The original continental 
masses should trend generall3" with the meridian. This is 
the fact with North America, South America, Greenland 
and Africa. Moreover, an ancient Scandinavian continent 
stretched from Spitzbergen to the Straits of Dover, while 
most of other parts of Europe were sea bottom. The 
ancient, but now much wasted continent which embraced 
Australia, New Guinea, Borneo and the Philippine Islands, 
had a submeridional trend. The Mascarene continent, 
including Madagascar, stretched north and south. The 
group of New Zealand islands, with the contiguous sub- 
marine mass, is elongated meridionally. (2) The great 
ocean basins and their submarine topography should 
reveal a similar influence. x\ccordingly the Atlantic and 
Pacific have their longer axes north and south, and the 
submarine topography of the Atlantic, so far as known, 
generally corresponds. As to the configuration of the 
Pacific Ocean, Prof. J. D. Dana pronoulices it "remark- 
able," and calls attention to the fact that "nearly all the 
ranges of islands over the Pacific Ocean, and even the 
longer diameters of the particular islands, lie nearly paral- 
lel with the great mountain ranges of the Pacific coast of 
North America." This arrangement he refers to the 
structure of the infra- Archaean crust. The method of sub- 



THE EARTH. 353 

sidence of the coral islands over a breadth of more than a 
quarter of the earth's circumference develops similar and 
parallel trends.* (3) Many accessory features of land 
and water might be expected to retain traces of early 
geognostic conformations now partially obliterated. I 
think we may discover these in the basin of Hudson's Bay 
and the seas and sounds stretching thence northward to 
the Arctic Ocean; in Baffin's Land and Baffin's Bay; in 
the valleys of the St. Lawrence, Mackenzie and Mississippi 
Rivers, and the Nile, Volga, Ural, Obi, Yenesei, Lena, 
Indus, Ganges, Brahmaputra and others; in the general 
trend of the West Indian Islands; in the form of Great 
Britain and the contiguous islands, in the Baltic, the Red 
and Caspian Seas ; in Novaya Zemlia and the Gulf of 
Obi; in Kamtchatka, the Sea of Okhotsk, the Japan Sea, 
the Yellow Sea; in the great alternating bays and penin- 
sulas of the south of Asia; and finally, in the north and 
south trends of minor features which have been deter- 
mined immediately by the strike of geological formations, 
such as the Adriatic, the ^gean and the Italian peninsula. 
Lakes Tanganyika and Albert Nyanza in Africa, and in 
Lakes Michigan and Huron and in Saginaw, Georgian, 
Thunder, Green and Grand Traverse Bays pertaining to 
these lakes in North America. 

But there are many terrestrial features which do not 
conform to the requirements of this theory. In reference 
to these there are two observations to be made: (1) When we 
regard the general expression conveyed by the aggregate 
of the earth's surface features, we find that the general 
meridional impress is unmistakable, (2) The meridional 
features are generally connected with the most primitive 
geognostic condition, and the transmeridional features can 
generally be shown to be of later origin, and to owe their 
existence to agencies which came into being only in the 

*Daua, 4.mer, Jour. Sci.^ in, v, 442-3, 
33 



354 SPECIAL PLAIs^ETOLOGY. 

later progress of the world's development. The most im- 
portant of these are: First, the transverse stretch of the 
continent of Enrasia. Now, when we look at a map of 
this continent we see that it is distinctly impressed by 
profound meridional characteristics. The numerous great 
rivers flowing northward along their several valleys almost 
interlock with the great bays projecting northward from 
the Indian Ocean. The general land area is clearly 
marked by a series of meridional rugosities, and the fact 
that the intervening depressions are now permanently 
above the sea level is an unimportant cirGumstan3e. Were 
this continent to undergo a subsidence, the waters of the 
Arctic and Indian Oceans would meet at several points. In 
confirmation of these views we learn that the oldest known 
rocks of China — the old Archaean gneisses — maintain a 
pretty uniform strike from north-northwest to south- 
southeast.* Further, it cannot be doubted that the lateral 
pressure of oceans has contributed greath^ to the develop- 
ment of folds along lines parallel with the ocean shores. 
This is an important part of the immediate agency which 
has uplifted so many coastwise mountain ranges. The 
ocean shore is indeed generally a feature which has been 
already determined by the movement of the primitive 
tidal swell; but if an ocean shore from any cause stretches 
across the meridians, contrary to the influence of the tidal 
swell, there must exist a strong motive for the development 
of transverse mountain ridges. Now such a relation exists 
between the mountains of central Asia and the Indian 
Ocean ; and between the Pyrenees, Alps, 'Carpathians and 
Caucasus, and the Mediterranean Sea — once much longer, 
broader and deeper than at present. Secondly, the moun- 
tains of central Europe and the Mediterranean Sea. The 
sea undoubtedly sustains some causal relation to these 
mountains, as well as the Atlas chain in north Africa, 

* Von Richthofeii : China, vol. ii. 



THE EARTH. 355 

But in its insular and littoral features we can even trace 
some relation to a deep-seated meridional structure. This 
is exemplified in the chain of Corsica and Sardinia; in the 
Italian peninsula and the Adriatic; in the ^gean; in the 
Syrtes Major and Minor, and in the truncated eastern ex- 
tremity. How the Mediterranean and Indian Ocean shores 
came to have o-eneral transmeridional trends is a question 
which must find its solution in the events of Mesozoic and 
Cf^nozoic geological history. It suffices to observe that 
the action which determined these shore lines belongs to 
medial and later geologic times, when the geotidal influ- 
ences had ceased to be active, and exerted themselves only 
in the form of a store of meridional predispositions which 
the powerful strains borne by a greatly thickened crust 
might well be supposed adequate to overcome. Thirdly^ the 
valley of the Amazons is a great transmeridional feature. 
It occupies, however, like the Amur, a great post-palfeo- 
zoic basin. This stretched southward from the mouth of 
the Amazons — like the ancient intra-Mediterranean pro- 
longation of the Gulf of Mexico stretching northward — 
and really constituted a primitive meridional feature, such 
as will probably be revealed in the geological structure of 
Asia. This southward basin seems to have been closed up 
in southern Brazil by the development of converging- 
ranges of mountains on the east and west limbs of South 
America; so that the present valley of the Amazons is 
merely the transverse dimension of an ancient depression 
at its widest part. 

3. The EartKs Aye, icit/i Methods of Calcidation. — 
As to the numerical expression of the age of the world, 
various guesses and calculated results have been given on a 
previous page (p. 179). The grounds of various estimates 
of the age of the world or of certain periods may be enu- 
merated as follows: 

(1.) The time required for the sun to contract from a 



356 SPECIAL PLAXETOLOGY. 

nebulous condition, or from the orbit of the earth to its 
present limits. / Professor Newcomb says the heat evolved 
by contraction from an infinite distance would last only 
18,000,000 years.* A temperature permitting the exist- 
ence of water on the earth would have been reached 10,- 
000,000 years ago. 

'^2.) The time which the sun will require to cool from 
its present condition to a darkened or planetary state^ 
Newcomb says the sun at its present rate of radiation will 
be as dense as the earth in 12,000,000 years; and it is 
quite likely to be long before that time that we are.to ex- 
pect the permanent formation of a continuous crust.f 

^ (3.)nrhe time required for the earth to cool from incipi- 
ent incrustation to its present state, based on the thermal 
conductivity of rock-masses and the rate of increase of 
heat toward the earth's centre^'^ Sir William Thomson con- 
cludes that this time cannot exceed 80,000,000 years. + 
Rev. O. Fisher, on a similar basis, calculates that the 
incrusted age of the world cannot exceed 33,000,000 years. 
M. Elie De Beaumont calculated that 38,359 years must 
have passed after the beginning of incrustation, before the 
rate of cooling in the general interior would surpass that 
of the crust. At this epoch the formation of mountains 
would begin. § 

'''(4.) Relative times required for the deposition of all 
the rocky sediments. / This method by itself furnishes no 
clew to absolute times, but only to time ratios. It makes 
the thickness of a bed of sediments the measure of the 
time consumed in its deposition. Undoubtedly, each bed 
is thus measured; but it cannot be assumed that a con- 
stant relation exists between time and thickness of sedi- 

* Newcomb: ropular Asfroaomy, 509. 
t Newcomb: Poiju'ar Astronomy, 51:3. 

t Thomson and Tait: Nat. Phil., 1st eel. Corap. Croll: Climate and Jltne, 
335. Fisher: Physics of the Earth's Crust, 71. 
§ De Beaumoi^t: Les Systtmes de Montagnes, 



THE EARTH. 357 

ments. At some epochs, and probably during whole 
periods and ages, the energy of the forces of deposition 
must have been more rapid than at other epochs and 
during other intervals of time. During the same interval 
the rate of deposition must be more rapid in one region 
than in another. This difference must arise from differ- 
ences in the activity of the same class of forces, and from 
differences in the kind of agency employed. Fragmental 
sediments accumulate more rapidly than calcareous; and 
the ratio of the two which is generally adopted regards 
one foot of limestones equivalent to five feet of sandstones 
or shales. 

Notwithstanding unavoidable inaccuracies, the method 
furnishes results of considerable value and interest. If 
the maximum thicknesses of the formations are taken from 
the same geognostic region, as for instance the region of 
Appalachian upbuilding, the ratio of the thicknesses may 
be nearly the same as in another region where the rate of 
accumulation is less. By taking the limestones from the 
same region we avoid exaggerating estimates for the same 
periods. The geognostic region of most active accumula- 
tion during Eozoic time was the Laurentian; that during 
PaljBozoic time was the Appalachian, and that during 
Mesozoic and Csenozoic time was the Rocky Mountain 
region and that of the Great Plains. Within each region 
we may assume the progress of sedimentation uniform. 
We do not know that the progress in one region during 
one time is comparable with the progress in another 
region during another time; but, so far as concerns shore 
action, we are compelled to assume it to be so. For 
instance, we must assume that ten thousand feet of Ter- 
tiary sediments accumulated by shore action in the Rocky 
Mountains correspond to the same length of time as ten 
thousand feet of the same kind of sediments, accumulated 
in the Appalachian region during Palaeozoic time. We 



358 SPECIAL PLAXETOLOGY. 

can understand, however, that the total sedimentation in a 
given length of time must have been greater in the later 
periods, when the land areas were more extensive, and 
river drainage brought larger contributions to the sea-bot- 
tom deposits. What allowance should be made for river 
action in the later ages it is impossible to state with any 
precision; but it will not probably exceed the require- 
ments to allow one-half from the fragmental deposits in 
the Tertiary lakes and seas of the Rocky Mountain region, 
and one-fifth from the fragmental deposits of the Mesozoic 
ao'es of the same reg-ion. 

This general method of determining time ratios has 
been employed by Professor James D. Dana,* who gives 
the following table for maximum thicknesses along the 
Appalachians: 

Fragmental Limestones. 

Eocks. 

1. Potsdam Period .... 7,000 200 

2. Rest of Lower Silurian 18,000 6.000 

3. Lower Silurian Era 25,000 6,200 

4. Upper Silurian Era 6,760 600 

5. Devonian Age 14.300 100 

6. Carboniferous Age 16,000 125 

Totals, feet 87,060 13,225 

Supposing limestones accumulate at one-fifth the rate 
of fragmental sediments, the above numbers become 
respectively (1) 8,000; (2) 48,000; (3) 56,000; (4) 9,760; 
(5) 14,800; (6) 16,625. These numbers have nearly the 
ratio of 1 : 6 : 7 : 11 : 2 : 2. "Hence, for the Silurian, 
Devonian and Carboniferous ages, the relative duration 
will be 8J : 2 : 2, or not far from 4:1:1. Or, the Silu- 
rian Age was four times as long as either the Devonian 
or Carboniferous; and the Lower Silurian Era nearly six 
times as long as the Upper Silurian." 

For the Mesozoic, Professor Dana announces the time 
ratios as, Triassic 1 : Jurassic \\ : Cretaceous 1. For the 

*Dana: Manual of Geology, Sded.. 381, 481, 585, 



2. Lower PalaBozoic. 



4. Neozoic 



TEE EARTH. 359 

Ca^nozoic he finds the maximum thickness of the Tertiary 
deposits 16,000 feet, with very little limestone. But as 
river action increased with enlargement of the land areas, 
he reduces this thickness one-half to arrive at the approxi- 
mate amount of marine sedimentation. Then, assuming 
the Quaternary to have been one-third as long as the 
Tertiary, he gets the ratios. Palaeozoic 12 : Mesozoic 3 
: Cagnozoic 1. 

The following table of the approximate thickness of 
the several geological formations in Europe — making no 
discriminations for limestones or for fluvial contributions 
— has been compiled by Rev. S. Haughton, of the Uni- 
versity of Dublin : * 

Feet. 
1. Eozoic 26,000 

Lower Silurian 25,000 

Upper Silurian 5,500 

Devonian 9,150 

3. LTpper PaljBozoic. -J Carboniferous 14,600 

(Permian 3,000 

fTriassic -. 2,200 

Jurassic 4,590 

Cretaceous 11,283 

Numinulitic [Middle Eocene] 3,000 

[Tertiary 6,000 

110,323 
From this, by disregarding Quaternary and including 
the Nummulitic in the Caenozoic, we get the ratios, Eozoic 
4.7 : I-ower Silurian 4.5 : Upper Silurian 1 : Upper Pa- 
laeozoic 4.9 : Mesozoic 3.3 : C^nozoic 1.6. 

In attempting to compile results from the latest deter- 
minations of thickness in the several formations, nothing 
better can be done than to accept for the Eozoic Great 
System, the conclusions of Sir William Logan for the 
Laurentian region. These give us for the maximum 
thickness of the Laurentian 30,000 feet, of which lime- 
stone masses aggregate 3,500 feet, or, deducting inter- 
calated beds of gneiss, 2,800 feet. For the Huronian, 
t Haughton, Phil. Mag., xxvi, 545, Dec. 20, 1877. 



360 SPECIAL PLAXETOLOGY. 

Logan's estimate was a maximum of 20,000 feet, with 
only thin layers of somewhat impure limestone, which 
we may set down at 100 feet. 

Turning to the Palaeozoic ages and the Appalachian 
region, in its extension to Nova Scotia, we may deduce 
the following statement of maximum thicknesses: 

PEmoEDiAL Group. — Acadian attains 10,000 feet in 
the Ocoee slates and conglomerates of east Tennessee. 
Potsdam, 5,600 feet of limestones, sandstones and shales 
in Newfoundland, of which 200 feet may be set down as 
limestones. Total fragmental, 15,408; limestone, 200. 

Canadian Group. — Calciferous attains 7,000 feet in 
east Tennessee, of which 3,000 feet are fragmental and 
4,000 feet chiefly limestones. Quebec, 6,600 feet in New- 
foundland, including 3,200 feet of limestone. Chazy, 
600 feet in east Tennessee, principally limestone. Total 
fragmental, 6,400 feet; limestone, 7,800. 

Teextox Group. — Trenton, in east Tennessee, 2,000 
feet of limestones and shales, of which 500 feet may be 
assumed as shales. Utica, 700 feet of shales in Pennsyl- 
vania. Hudson River, 1,259 feet of limestone at Anti- 
costi, or 2,000 feet of shales near Quebec, or 6,000 feet of 
shales in Pennsylvania.* Total fragmental, 7,200 feet; 
limestones, 1,500 feet. 

Niagara Group. — Jlediiia attains 2,500 feet of con- 
glomerates and sandstones in Pennsylvania. Clinton, 
2,555 feet of shales in Pennsylvania. Kiagara, in Pennsyl- 
vania embraces 450 feet of marl or fragile shale, and 1,200 
feet of the same with thin limestone layers. Consists 
of 350 feet of limestone in Iowa, which is nearly equiv- 
alent. Total fragmental, 6,605 feet; limestones, 100 feet. 

Salixa Group presents a maximum of 1,650 feet in 
Pennsylvania, of which not over 100 feet can be set down 
as limestones. 

* Lesley: 2d Penn. Survey, G 6, p. 152. 



THE EAKTH. 3G1 

Lower Helderberg Group presents a maximum at 
Cape Gaspe of about 1,500 feet of limestones. 

Oriskany Group attains 520 feet of calcareous shales 
and argillaceous sandstones in Pennsylvania, of which not 
over 50 feet could be counted as limestone. 

CoRNiFEROus Group. — Cciuda Gain (rW^ attains 300 
feet in eastern Pennsylvania, and Corniferous limestone 
500 feet in northwestern New Jersey. 

Hamiltox Group. — The Gaspe sandstones present a 
maximum of 6,000 feet. Otherwise we might take the 
Marcellus shale, with some argillaceous limestone, in 
Pennsylvania, at 1,300 feet (I. C. White) — not over 50 
feet limestones — the Hamilton proper in Pennsylvania, at 
1,375 feet (I. C. White) of shales and sandstones, and the 
Genesee, also in Pennsylvania, at 700 feet of black calca- 
reous shale (not over 50 feet limestone), making fragmental 
3,275 feet, and limestone 100 feet. But we shall adopt the 
Gasp6 measure. 

Chemung Group. — Portage amounts to 1,700 feet of 
flaggy sandstones and blue shales in Pennsylvania. Che- 
mung, 3,200 feet of sandstones, shales and conglomerates 
along the Appalachians. Total, 4,900 feet fragmental. 

Catskill Group aggregates 6,000 feet of sandstones, 
shales and conglomerates along the Appalachians, reaching 
7,544 feet in Carbon county, Pennsylvania, all of which is 
fragmental except 14 feet of calcareous breccia. 

Lower Carboniferous series in Pennsylvania ag- 
gregates 5,560 feet of shales and sandstones with some 
(say 500 feet of) limestones. On the eastern border, 
6,000 feet of sandstones, marls, marlites and gypsum; in 
Tennessee and Alabama, 2,170 feet of limestones, which 
is equivalent to 10,850 feet fragmental. It may be best 
to adopt the Pennsylvania measure, which gives frag- 
mental, 5,010; limestone 500. 



362 SPECIAL PLAl^ETOLOGY. 

Upper Carboniferous series. — Maximum tnickness of 
Coal Measures in Nova Scotia, 14,570 feet (in Pennsyl- 
vania, 9,000 feet and over). 

Turning next to the Mesozoic and Tertiary ages, the 
following statement of maximum thicknesses is afforded 
by the most recent investigations. 

Triassic. — Koipato Group, of the West Humboldt 
Range, 6,000 feet, strictly non-calcareous. Star Peak 
Group, 6,300 feet of quartzites, and 4,600 feet of lime- 
stone (King). Total fragmental, 11,300 feet; limestones, 
4,500 feet. 

Jurassic. — In the West Humboldt Range, 1,800 feet 
of impure limestones and 4,000 feet of shales. Say frag- 
mental, 4,800 feet; limestones, 1,000 feet. 

Cretaceous. — In the Uinta region: Dakota^ 500 feet 
of sandstones and clays; Colorado, 2,000 feet of clays, 
marls and some (say 100 feet of) limestone; Fox HillSy 
4,000 feet of sandstones (King). Total fragmental, 6,400 
feet; limestones, 100 feet. 

Tertiary. — Laramie, in Green River Basin, 5,000 
feet, mostly sandstones. Wahsatch, in Rocky Mountains, 
5,000 feet of marls and sandstones. Green River, in 
southwestern Colorado (Cope), 2,670 feet of shales. 
JBridger, 5,000 feet of argillaceous and arenaceous strata. 
Uinta, 600 feet of grits and conglomerates, in Uinta Range. 
White River Group, 2,000 feet of calcareous clays, 
alternating with sandstones, in Wind River Mountains. 
Truckee Groups, 4,000 feet, chiefly of indurated, trachytic 
mud. Loup River Group, 2,000 feet of sandstones, on 
the Great Plains. North Park Group, 300 feet of sandy 
and marly deposits. Total fragmental, 26,470 feet; lime- 
stones, 100 feet. 

From these results may be compiled the following table 
of maximum thicknesses: 



THE EARTH. 363 

Fragmental. Limestones. 

EOZOIC 47,100 2,900 

Laurextian 27,200 2,800 

HURONIAN 19,900 100 

PALAEOZOIC 75,999 12,250 

SiLURiAX 37,155 11,200 

Lower Silurian 29,000 9,500 

Primordial 15,400 200 

Canadian 6,400 7,800 

Trenton 7,200 1,500 

Upper Silurian 8,155 1,-700 

Niagara 6,605 100 

Salina 1,550 100 

Lower Helderberg 1,500 

Devonian 19,214 550 

Oriskany 470 50 

Corniferous 300 500 

Hamilton 6,000 

Chemung 4,900 

Catskill 7,544 

Carboniferous 19,630 500 

Lower Carboniferous 5,060 500 

Upper Carboniferous 14,570 

MESOZOIC 22,500 5,600 

Triassic 11,300 4,500 

Jurassic 4,000 1,000 

Cretaceous 0,400 100 

Tertiary 22,470 100 

Total stratified rocks to Quaternary. .168,069 20,850 

Fragmental and calcareous 188,919 feet. 

To arrive at a truer expression of time ratios, we must 
probably diminish Mesozoic fragmental deposits one-fifth, 
and Tertiary deposits perhaps one-half, and increase all 
calcareous strata five-fold. The combined results give the 
numbers entered, on a following page, in the table of the 
"Estimated Length of Geological Periods." These, for 
the sake of easier comparison, are reduced to percentages 
in another column. 

From this table it appears that the Lower Silurian was 
4.6 times as long as the Upper Silurian; the Devonian 
was nearly one-fourth the duration of the Silurian; and 
the Carboniferous was as long as the Devonian. The 
Palseozoic was 3^ times the length of the Mesozoic and 
9^ times the Caenozoic. The Tertiary was one-ninth of the 
time since the lower Silurian, while Sir Charles Lyell 



364 SPECIAL PLAN^ETOLOGY. 

makes it one-fourth the time since the Cambrian.* Ram- 
say makes the Devonian and Triassic united equal to the 
Jurassic, Cretaceous and C^^nozoic;! but the tabular 
ratios here determined make the former 2^ times the 
latter. The Tertiar}'', it appears, was one-sixteenth the 
Mesozoic and Palaeozoic united; while Professor Dana 
makes it one-fifteenth. J; 

With a view to arriving at some absolute measure of 
geological periods, we may assume Post-Tertiary time to 
be one-fourth as long as Tertiary. § We may also assume 
the Glacial epoch to be two-thirds of the Post-Tertiary; 
and may further assume the Azoic period of the earth's 
sedimentary history to be equal to the Eozoic; and the 
pyrolithic or presedimentary incrustive history to be equal 
to the Azoic and Eozoic united, and here designated 
Archaean. We are thus furnished with an expression for 
the incrusted age of the world in terms of sediments, and 
may, for convenience, calculate a percentage value for each 
interval as shown in one of the columns of the table 
referred to. These are the final time ratios. If we assume 
the whole incrusted age of the vvorld as 80,000,000 years, 
according to Sir William Thomson, the time to be allotted 
to each period is such as shown in another column of the 
table. If, again, according to Professor Newcomb, we 
allow 10,000,000 years for the time since sedimentation be- 
gan, which, calculating from the tabular time ratios, makes 
13,844,662 years for the time since incrustation began, we 
get the series of values given in the last column of the table. 

* Lyell : Principles of Geology, 10th ed. 

tKamsay, Proc. Roy. Soc, So. 15-2, 1874. 

tHe, however, counts the Laramie with Mesozoic, while here it is regarded 
as Tertiary. My former convictions, in accord with the views of Marsh and 
Cope, have been liere abandoned in deference to the recent positive statements 
of C. A. White. (Amer. Jour. Sci., Ill, xxv, 207-9.) 

§Prof. Dana puts the Post-Tertiary equal to one-third of the Tertiary: but 
he does not include the Laramie group in the Tertiary, nor does lie accord the 
Tertiary accumulations the enormous thickness which they have recently been 
shown to possess. 



THE EARTH. 365 

ESTIMATED LENGTH OF GEOLOGICAL PERIODS. 



Formations. 



PYROLITHIC 

ARCHAEAN 

Azoic 

Eozoic 

Laurentiaii 

Huronian 

Paleozoic 

Silurian 

Lower Silurian 

Primordial 

Canadian 

Trenton 

Upper Silurian 

Niagara 

Salina 

Lower Helderberg . 

Devonian 

Oriskany 

Corniferous 

Hamilton 

Chemung 

Catskill 

Carboniferous 

Lower Carboniferous . 
Upper Carboniferous. 

Mesozoic 

Triassic 

Jurassic 

Cretaceous , . . . 

C.^xozoic 

Tertiary 

Post-Tertiary 

Glacial 

Post-Glacial 

Total Crust 



Rock 

MEASURE, 

feet. 



123,200 
123,200 
61,600 
61,600 
41,200 
20,400 

137,244 

93,150 

76,500 

16,400 

45,400 

14,700 

16,650 

7,100 

2,050 

7,500 

21,964 

720 

2,800 

6,000 

4,900 

7,544 

22,130 

7,560 

14,570 

45,360 

31,540 

8,200 

5.620 

14,669 

11,735 

2,934 

1,956 

978 



443,673 



Per- 
cent- 
age. 



^7.77 
27.77 
13.88 
13.88 
9.26 
4.62 

30.93 

21.00 

17.25 

3.70 

10.23 

3.32 

3.75 

1.60 

.46 

1.69 

4.96 

.17 

.63 

1.35 

1.11 

1.70 

4.98 

1.70 

3.28 

10.22 

7.11 

1.85 

1.26 

3.31 

2.65 

.66 

.44 

9.9. 



100.00 



Thomson's 
Basis, 

years. 



22,216.000 
22,216,000 
11,104,000 
11,104,000 
7,408,000 
3,696,000 

24,744,000 

16,800,000 

13,800,000 

2,960,000 

8,184,000 

2,656,000 

3,000,000 

1,280,000 

368,000 

1,352,000 

3,968,000 

136,000 

504,000 

1,080.000 

888,000 

1,360,000 

3,984,000 

1,360,000 

2,624,000 

8,176,000 

5,688,000 

1,480,000 

1,008,000 

2,648,000 

2,120,000 

528,000 

352,000 

176,000 



80,000,000 



Newcomb' 
Basis, 
years. 



3.845,000 
3,845,000 
1,922,000 
1,922,000 
1,282,000 
639,000 

4,282,000 

2,907,000 

2,388,000 

512,000 

1,416,000 

460,000 

519,000 

221,000 

64,000 

234,000 

686,700 

23,500 

87,000 

186,900 

153,700 

235,400 

689,500 

235,400 

454,100 

1,415,000 

984,400 

256,100 

174,400 

458,300 

366,900 

91,370 

60,920 

30,460 



13,845,000 



It can hardly be doubted that the total thickness of the 
Laurentian and Huronian series of strata is much greater 
than has been observed or estimated. Few, I think, would 
hesitate to admit that Eozoic Time was as long as Lower 
Silurian, but our table only makes it about four-fifths as 



366 SPECIAL PLAXETOLOGY. 

long. It is not at all improbable that some large portion 
of the primitive strata designated Azoic, as well as the 
entire Pyrolithic crust, has been removed through ascent 
of the isogeothermal planes, so that the remaining thick- 
ness, even if measurable, would not afford a correct rela- 
tive measure of Pyrolithic and Archaean time. The effect 
of an augmentation of P^^rolithic and Archaean time would 
be a diminution of the relative length of all the later 
periods. It may be mentioned, on the contrary, that 
strong probability exists, as before shown, that the accu- 
mulation of sediments was more rapid in primitive times 
than during the later periods. The shorter year, the more 
rapid rotation of the earthy the superior tidal efficiency of 
the moon and sun, not to mention more energetic chemical 
action, all disclose the existence of geological forces which 
must have acted, in remote times, with a degree of energy 
for which the agencies of modern times present no ade- 
quate measure. These facts point toward a diminution of 
the ratios for remote ages, and an increase of those for 
later times. This would raise the numerical value of post- 
glacial time above the figures indicated by more direct, 
and apparently more trustworthy estimates remaining to 
be noticed. The alternative is therefore to diminish the 
whole time allowed since incrustation and sedimentation 
began. 

^ (5.) Calculation based on the obliteration of the rota- 
tional effects of the upheaval of a continental mass. / Rev. 
S. Haughton has attempted to calculate a minor lirnit for 
the time since the elevation of Europe and Asia, at the 
end of the Nummulitic epoch.* He shows that the uplift 
of this continental mass must have displaced the axis of 
maximum inertia of the earth through sixty-nine miles, 
in the direction of the meridian of the Andes. The axis 
of rotation would thus acquire a motion on the surface of a 

* paughton: Philosophical Magazine, December 20, 1877, 534-46. 



THE EARTH. 367 

right cone around the axis of figure, with its pole at the 
distance of sixty-nine miles from the pole of the axis of 
figure; and this motion would be perpetual unless de- 
stroyed by friction. But the place of the ocean would 
always be slightly behind the place of the rigid earth, 
and some friction would constantly result, which would 
tend to destroy the wabbling movement of the earth. As 
astronomy is now unable to detect any such movement, 
though the precision of its instruments should detect 
a wabble of five feet (instead of sixty-nine miles), the 
problem is presented, What time has been occupied in the 
destruction of the wabble? From researches on tidal fric- 
tion,* which causes a retardation amounting to one sec- 
ond in the length of the day in 100,000 years, Professor 
Haughton now calculates that if Europe and Asia were 
suddenly elevated, a wabble of sixty-nine miles would re- 
quire 640,730 years for its extinction. If they were 
formed by sixty-nine geological uplifts, each of which dis- 
placed the axis of figure through one mile, then, supposing 
the radius of the wabble to be reduced from one mile to 
five feet in the interval between each two successive convul- 
sions, the minimum time required for the extinction of the 
wabble would be 27,491,000 years. If, again, the rate of 
upheaval of Europe and Asia was so slow that the increase 
of the radius of an assumed wabble of five feet was exactly 
destroyed by friction during each wabble, then the total 
time required for the production of Europe and Asia 
would be 4,170,000 years.f 

*Delaunay: Sur le Raleniissement de la Rotation de la Terre. Paris, 1866. 

tit is erroneous to assume Europe and Asia produced entirely after the 
close of the Nummulitic epoch. This mid-Eocene disturbance elevated the 
Pyrenees, the Julian Alps, the Appenines and Carpathians, and probably ex- 
tensive regions in Northern Africa, and through Central Asia as far as Japan 
and the Philippine Islands. But large masses of the European continent rose 
at intervals during Palaeozoic and Mesozoic time. So that the period of the ex- 
tinction of the wabble may have extended back far beyond the close of the 
Nummulitic epoch —a necessity provided for in the secoi>d and third supposi- 
tions of Professor Haughton. 



368 SPECIAL PLAJ^^ETOLOGY. 

Professor Haughton now attempts to employ the unit 
thus obtained in the calculation of the length of the 
earth's sedimentary history. To do this, he compiles the 
table of rock thickness before quoted, and then on the 
principle, 

m X 1 T X Total thickness of sediments ,, rri- 

Total sedimentary age = Thickness of Tertiary rocks >< ^^^^e repre- 

sented by Tertiary rocks, 

he assumes the minor limit given above under the first 

supposition, and gets 

110,323 ^ (340 -J.3Q ^ 11^00,000 years. 



6,000 

This approximates Professor Newcomb's calculation of 
the sedimentary age of the world. 

Since, however, it can hardly be assumed that Europe 
and Asia were uplifted per saltum, the above result for 
the sedimentary age of the world must be too small. If 
the formation of the continent occupied a million years, 
the total duration of sedimentary time would be nearly 
37,000,000 years. Manifestly, however, the succession of 
uplifts extended back into Pre-Nummulitic time, so that 
the unit obtained cannot be regarded as representing 
Post-Nummulitic time. 

^(6.) The time since the middle of the last glacial 
period, based on the theory that epochs of glaciation on 
the northern hemisphere have been caused by extreme 
eccentricity of the earth's orbit^/^This theory has been 
carefully expounded by Professor CrolL* The last occur- 
ring epoch of maximum eccentricity, according to Stock- 
well's calculations \ (supplemented by CroU's) were, before 
1800 A.D., 100,000 years, 210,000 years, 310,000 years, 
750,000 years and 850,000 years. Those at 210,000 and 
850,000 years are the most striking. Professor Croll 
regards the last glacial period as extending from 240,000 

* Croll: Climate and Time. 

iStoc\i\\e\], Smithsonian Contributions to Knowledge, -^ym; K. W. McFar- 
land, Amer. Jour. Sci., Ill, ?;i, 456, 
24 



THE EARTH. 369 

to 80,000 years ago. The maximum of 850,000 years, he 
thinks, fell in the Miocene period; and a maximum at 
2,500,000 years ago he regards as belonging to the 
Eocene. If, according to Croll, the advent of the last 
glacial period occurred 240,000 years ago, this number 
represents Post-Tertiary time, which, according to the 
foregoing table, represents 0.4 of one per cent of the 
whole time since incrustation began, and would make that 
time 60,000,000 years. Again, if 2,500,000, according to 
Croll, represents the time since the beginning of the Ter- 
tiary Age, the whole incrusted age of the world would be 
131,600,000 years, which I do not feel disposed to allow. 
If 100,000 years be taken as marking the tniddle of the 
last glacial epoch, then by the same table of ratios, the 
incrusted age of the world would be 33,000,000 years. 
Even this is 18,000,000 years more than Professor New- 
comb's calculation allows when combined with the above 
tabular ratio for the Pyrolithic Aeon. 

(7.) Estimates based on rates of erosions and deposi- 
tion. The Niagara gorge has exercised the wits of a long 
series of observers. Mr. Robert Bakewell assumed the 
rate of recession to be three feet a year, from which he 
calculated the age of the gorge, seven miles in length, to 
be 12,300 years.* Messrs. Lyell and Hall, assuming a 
rate of one foot a year, obtained a result of 35,000 years.f 
Mr. E. Desor, on an assumed rate of .03 foot per annum, 
made the age of the gorge 1,232,000 years. Mr. Jules 
Marcou,J; in 1863, found a recession of twelve feet in the 
Canadian fall at the base of the "Terrapin Tower," since 

*R. Bakewell: Introduction to Geology, 260; Loudon's Magazine of Nat- 
ural History, 1843-4. 

+ Sir Charles Lyell, Proc. Geol. Soc, London, 1842, 1843; Travels in North 
America, 1st Visit, ch. ii; Principles of Geol., 8tli ed.. 205; James Hall, Boston 
Jour. Nat. Hist., 1843-4; Geol. Fourth Dist. New York, ch. xx, 1843. 

t Jules Marcou, Bulletin de la Sac. geol. de France, II, xxi, 290-300, 529, two 
plates. See also Ramsay, Quar. ./our. Geol. Soc, xv, 212, 1859, who thinks the 
falls commenced during the deposition of the "Leda Clay,"' or a little before the 
close of the Drift period. 



370 



SPECIAL PLAXETOLOGY. 



the trigonometrical survey, executed under the direction 
of Professor James Hall in 1842. This is a recession of 
.57 foot per annum at that point, and implies, if applied 
to the entire gorge, a period of 64,842 years. Mr. Thomas 
Belt,* after a careful examination, assumed the rate of 
recession at .01 foot per annum. But he announced the 
important discovery, if a fact, that the ancient gorge, 
from the whirlpool to St. David's, on the Canadian side, 
now filled with gravel, was excavated in pre-glacial times; 
and the old gorge apparently extended, also, up nearly to 
the present falls. In this view, the only post-glacial work 
is included between Queenston and the whirlpool, with 
the addition of an unknown, but probably small, portion 
of the gorge above the 
whirlpool. Mr. Belt as- 
sumes, however, in round 
numbers, that 20,000 
years express the maxi- 
mum limit of time since 
the commencement of the 
new gorge at Queenston. 
His own assumption of the 
rate of recession would 
give for the three miles be- 
low the whirlpool, 158,000 
years, which, as Mr. Belt 
recognizes, is more than 
the time at our disposal 
for the incrusted history 
of the earth will allow. 
The accompanying dia- 
gram will illustrate Mr. 
Belt's views. 




Fig. 53. 



Mr. James T. Gardner, 



Niagara Gorge- 
New. 



•Old and 



♦Thomas Belt, (^uar. Jour, of Science, April, 1875. 



THE EARTH. 371 

Director of the New York State Survey, has given atten- 
tion to the rate of recession of Niagara Falls, reproducing 
Hennepin's narrative and illustration, and the map of the 
triangulation of 3 8-42, by Mr. Blackwell.* On the lat- 
ter he has laid down also the line of the falls as deter- 
mined by the United States Lake Survey in 1875. f From 
this comparison is shown "the unexpected fact that the Horse 
Shoe Falls have receded, in places, 160 feet during thirty- 
three years, and that a large island has disappeared which 
formerly existed in the midst of the Canadian Rapids." In 
spite of some slight inaccuracy resulting from the indepen- 
dent datum points of the surveys of 1842 and 1875, the errors 
cannot be so great, as Director Gardner informs me, that 
the assumption of a recession of 100 feet in thirty-three 
years would involve any degree of uncertainty. This is 
an average of three feet a year, and implies 12,320 years 
for a gorge seven miles long. For the three miles below 
the whirlpool, this rate of recession requires 5,280 years, 
which, adding for some amount of work above the whirl- 
pool, comes strikingly near to other estimates of post- 
glacial time, presently to be mentioned. At the same 
time, this is by far the most trustworthy determination 
ever made of the rate of recession of the Falls. 

It may be added that I find it stated in the public 
prints that great changes took place at the Falls during 
1880, and these were especially commented on at the 
annual meeting of "old settlers." The Canadian Fall is 
said to have changed more during the preceding year 

* J. T. Gardner: Report of New York State Survey fm' the Year 1879. 

tBy a remarkable oversight the triangulation of the Lake Survey was not 
connected with the survey of 1842; although the permanent landmarks of the 
earlier survey were perfectly accessible, and such connection only was needed 
to shed important light on a highly interesting problem. The mutual adjust- 
ment of the two triangulations was made by Director Gardner in 1879; and 
while, as he writes (Feb. 21, 1883), the accuracy attainable is not as great as if 
the two triangulations had been referred to the same datum points, it is safe to 
assume that the true relative positions of the Horse Shoe Falls in 1842 and 1875 
are shown without a probable error greater than twenty feet. 



372 SPECIAL PLANETOLOGY. 

than during the twenty or thirty years previous. The 
Fall, *'in the centre, has fallen back some 75 to 100 feet." 
Without claiming for these figures any considerable ex- 
actness, they may apparently be received as evidence of a 
more rapid recession than most students of the Falls have 
admitted, and they are strongly sustained by Mr. Gard- 
ner's more scientific determinations. 

The gorge of the Mississippi River below the Falls of 
St. Anthony has been studied by Professor N. H. Win- 
chelL* This, he argues, is entirely a post-glacial erosion 
as far as Fort Snelling. The mean rate from 1680 to 1856 
appears to have been 5.15 feet a year, so that the time 
required for recession from Fort Snelling, eight miles, is 
8,202 years. The date of the commencement of this part 
of the gorge, according to the geological indications, was 
"near the acme of glacial cold, or, at least, when the €^f^ect 
of that cold on the superficial accumulations was greatest." 

Various estimates have been framed of the rate of 
deposition in deltas. Elaborate investigations have been 
made of the Mississippi delta under the auspices of the 
United States government. Messrs. Humphreys and 
Abbott,! by a careful comparison of the volume of the 
delta deposit with the volume of sediment transported 
annually to the Gulf of Mexico, estimate the age of the 
delta to be about 5,000 years. This, of course, supposes 
uniformity in the rate of deposition, and expresses the 
time since the adjustment of the present drainage system, 
and not since the /*acme of glacial cold." 

Similarly, the age of the Nilotic delta has been set 
down at 6,350 years. J 

♦N. H. Winchell, Quar. Jour. Geol. Soc, London, Nov., 1878, 880-901: 
Fifth Ann. Report Geol. Minn., 1876. See digest in Southall's The Epoch of 
the Mammoth, ch. xxiii. 

+ Humphreys and Abbott: Hydraulics of the Mississii)pi, 1861. But see 
also E. W. Hilgard, On the Geology of Lower Louisiana, and the Sock Salt De- 
posit of Petite Anse, Proc. Amer. Assoc, 1868, 32T-40. 

X De Lanoye : Ramses the Great. 



THE EARTH. 373 

A recent writer calculates that the sediments of the 
three great rivers of China would fill the Yellow Sea and 
the Gulfs of Pe-chili and Lian Tung in 24,000 years; and 
in 36,000 years would extend the continent to its ancient 
limit at the 129th meridian, and south to the 29th paral- 
lel.* 

The rate of continental erosion and consequent subsi- 
dence has been much studied within a few years. The 
following are some results. The surface is calculated to 
subside one foot in the basin of the Plata in 29,400 years ;f 
in the basin of the Pei-ho in 25,218 years; | in the basin 
of the Thames, 9,600 years ;§ in the basin of the Danube, 
6,846 years; || in the basin of the Mississippi, 4,640 
years ;1^ in the basin of the Nile, 4,723 years; in the 
basin of the Yang-tse, 3,707 years;** in the basin of the 
Ganges, 1,751 years;ff in the basin of the Rhone, 1,528 
years ;tt the Hoang Ho, 1,464 years ;§§ the Po, 729 years ;|||| 
in the basin of the three great rivers of China, the Yang- 
Tse, the Hoang-ho and Pei-ho, 1,687 years.'^IT The general 
surface of England and Wales is estimated to subside by 
erosion one foot in 13,000 years, and the continental sur- 
face of Europe at large, one foot in five hundred million 

*H. B. Guppy, Nature, xxii, 488. Mr. A. Woeikoff thinks the first period 
should be extended to 28,000 years. Nature, xxiii, 9. 

t Higgins. But see T. M. Reade, Nature, xxii, 559 ; Guppy, Nature, xxiii, 35. 

X Guppy : loc. cit. 

§Geikie; Huxley: Physiography; but see T.M.Heade, Nature, xxii, 559. 
J. Prestwich calculates that the matters in solution in the Thames are sufficient 
to lower the surface of the Thames basin one foot in 13,000 years. Address as 
President Geol. Soc, Feb., 1872, abstract, Amer. Jour. ScL, HI, iv, 413. 

II Geikie: Man. Geol., ch. xxv. 

scroll says 6,000 years (Climate and Time, 330), and so says Geikie. Mr. 
A. Tylor says one foot in 10,000 years (Phil. Mag., 1850). 

**H. B. Guppy, Nature, xxii, 486-8; but see A. Woeikoff, Nature, xxiii, 9. 

tt Geikie says 2,358 years {op. cit.), and so says Croll ( Climate and Time, 331). 
See also. Amir. .Jour. Sci., Ill, xii, 458. 

XX H. B. Guppy, Nature, xxii, 488. 

§§ Geikie. 

nil Geikie. 

tt Guppy. On river sediments see Reclus : The Earth, ch. lii-iv. 



374 SPECIAL PLAXETOLOGT. 

years.* Prof. Croll, on the basis of a much more extended 
examination, and a juster apprehension of the whole range 
of evidence, concludes that the general surface of the land 
is subsiding by erosion at the rate of one foot in five or six 
thousand years. 

It is manifest that the action of water in lowering the 
surface of the land is two-fold, mechanical and chemical, 
and that investigators have not generally taken this fact 
into account, since they have studied chiefly the effects of 
erosive action as revealed in sediments. But chemical 
solution, of calcareous matters especially, amounts, in 
some regions, to almost as much as the processes of sur- 
face denudation, as Prestwich has shown for the basin of 
the Thames. Uniting chemical and mechanical agencies, 
the total diminution of the land must be much more rapid 
than is shown bv the foreo-oino- citation of results. 

(8.) The rate of Bluff-recession and Terrace-formation.^ 
Professor E. Andrews has made a careful study of the^ 
formation of the terraces and sand beaches bordering 
Lakes Michigan and Huron, esi^ecially in the neighborhood 
of Chicago and the southern extremity of Lake Michigan, f 
He finds, from the present rate of erosion (5.28 feet per 
annum), that 2,720 years have been occupied in the reces- 
sion of the bluffs which bound the lake at its present level. 
But above the bluffs are two successively higher sand 
beaches. By comparing their total contents with the con- 
tents of the modern beach (contemporaneous with the 
modern bluff, and therefore 2,720 years old), it appears 
that the two upper beaches have required 2,570 years for 
their accumulation. The sum of these numbers, 5,290 
years, represents the whole time elapsed since the close of 

*T. M. Keade: Address, Liverpool Geol. Soc, 1876: Xature, 26 Oct., 1876; 
Amer. Jour. Sci., m, xii, 462. Beyond 'question, this is a most extravagant 
estimate, and deserves citation merely as a curiosity. 

+ E. Andrews. Trans. Chicago Acad. Sciences, ii. See also digest of this 
memoir in Southall : The Epoch of the Mammoth, eh. xxii. 



THE EARTH. 375 

the glacial period. In other words, there is a bluff north 
of Chicago whose rate of recession has been ascertained 
by observation. The former position of the bluff has been 
learned by soundings in the lake, and therefore the whole 
volume removed, and the time required for the work. But 
the material removed has been redeposited in a terrace at 
the south end of the lake, whose volume has been meas- 
ured, and whose age must be the same as that of the bluff. 
There are also two terraces in the rear of the bluff, and by 
comparing their volume with that of the modern terrace 
whose age has become known, we get the time which 
elapsed after the formation of the lake and before the be- 
ginning of bluff-erosion. The age of the upper terraces 
united with the age of the bluff gives the time since the 
beginning of the Champlain epoch. Dr. Andrews con- 
cludes finally, that the true time must be somew^here from 
5,300 to 7,500 years. As this, according to the table of 
ratios previously given, is 0.22 per cent of the total time 
since the commencement of incrustation, the incrusted 
history of the world would be from 2,404,545 to 3,404,545 
years. 

It would not be surprising if Dr. Andrews had consid- 
erably underestimated the original volume of the sands 
in the two upper terraces. It is evidently their original, 
and not their present, volume which constitutes a measure 
of the time of deposition. But, since their abandonment 
by the lake, they have been exposed to all that wastage 
which, as we have seen. Professor Croll calculates to 
amount to one foot in 6,000 years. That is, supposing 
these upper sands to have been exposed 6,000 years, they 
have lost already one foot of their original depth. Due 
allowance for this wastage would lengthen the time re- 
quired for the upper beaches by an important percentage, 
raising it, perhaps, nearly as high as the figures obtained 
for the St. Anthony gorge. Still, the method pursued is 



376 SPECIAL PLAKETOLOGY, 

unimpeachable, and the result must be regarded as fairly 
approximative. 

(9.) Still another method of calculating the length of 
the last glacial period has been suggested by a passage 
in an address by Sir William Thomson.* "Any consider- 
able area of the earth, of say not less than a kilometer in 
any horizontal diameter, which, for several thousand years, 
had been covered by snow or ice, and from which the ice 
had melted away and left an average surface temperature 
of 13° C, would, during nine hundred years, show a decreas- 
ing temperature for some depth down from the surface; 
and thirty-six hundred years after the clearing away of 
the ice, would still show a residual effect of the ancient 
cold in a half rate of augmentation of temperature 
downward in the upper strata, gradually increasing to the 
whole normal rate, which would be sensibly reached at a 
depth of 600 metres." Now, all the northern portion of 
temperate America has been buried beneath snow and ice 
for a thousand years and much more, during which a 
greatly diminished rate of augmentation was established; 
and, unless the time since the disappearance of the ice has 
been sufficiently prolonged for the normal rate to be 
restored, there must still exist a slower rate of downward 
increase of temperature under the surface of Michigan, 
for instance, than under the surface of Louisiana. If the 
rate of increase could be well established for regions once 
glaciated, and also for regions not glaciated, the differ- 
ence in the rates would furnish a datum for calculating, 
on the principles employed by Sir William Thomson, the 
time since the uncovering of the glaciated areas. Even 
if no difference could be detected between Louisiana and 
Michigan, for instance, in consequence of the length of 
time since the disappearance of glaciers in Michigan, there 

* Sir Wm. Thomson, Address Brit. Assoc, Glasgow, 1870; Amer. Jour. Sd., 
Ill, xii, 340. 



THE EARTH. 377 

might be a difference in the rates in Louisiana and Win- 
nepeg, or Norway House or Fort Churchill. 

The best efforts of science thus far to arrive at a trust- 
worthy numerical estimate of the age of the world have 
been signally foiled by the impossibility of obtaining the 
value of certain constant quantities in the problem. One 
may feel predisposed to trust preferably the more mathe- 
matical methods, or those based on radiation, conduction 
and condensation, as likely to furnish the closest approxi- 
mation; since those based on rate of geological actions 
are liable to be vitiated by unsuspected and undiscover- 
able variations in the intensity of the action — all the 
more indeterminable because located in terrestrial periods 
separated by so many revolutions from the present ob- 
served order of events, which must furnish us our only 
rule of measurement. But even in the mathematical 
methods, it is indispensable to make enormous assump- 
tions, with nothing better than a general judgment to be 
our guide. On the whole, I am inclined to accord at least 
equal confidence to the simple methods which address 
themselves to the later results of geological action, where 
the energy of the forces must have been quite comparable 
with the action of recent times, which falls under our 
direct observation. Such methods are those depending 
on observed and measured rates of erosion of river gorges 
and lakeside and seaside bluffs. Among these we have 
four attempts which may fairly be regarded as approxi- 
mating exact solutions. These are: (1) The rate of 
recession of Niagara Falls, as lately announced by Direc- 
tor James T. Gardner, combined with the earlier sugges- 
tion of Mr. Belt in reference to the old gorge; (2) the 
rate of recession of the Falls of St. Anthony, as worked 
out by Professor N. H. Winchell; (3) the rate of recession 
of the lake bluff north of Chicago, and the determination 
of the volume of the upper terraces above the bluff; 



378 SPECIAL PLAXETOLOGY. 

(4) the age of the Mississippi River delta, as determined 
by Humphreys and Abbot. These four attempts are 
measurements of the time since the disappearance of the 
continental glacier, and the substantial agreement of the 
results adds to our confidence in them. The results are as 
follows : 

1. By Xiagara Gorge 5,280 years. 

2. By the St. Anthony Gorge 8,202 years. 

3. By Lake Michigan Bluffs 5,300 to 7,500 years. 

4. By the Mississippi River Delta 5,000 years. 

Now, when we recall that some time must be added to 

the result from the Niagara gorge for some small amount 
of work done above the whirlpool in post-glacial time; 
that the result from the lake bluifs must be increased in 
consequence of denudation of the upper terraces since 
they were first formed ; and that something must be added, 
also, to the result from the Mississippi delta, in conse- 
quence of a commencement somewhat later than that of 
the other works, it will appear that these various results 
are singularly accordant, and point toward 6,000 or 7,000 
years as the most probable interval since the commence- 
ment of the flood of post-glacial time. If we assume this 
at 6,500 years, the whole incrusted age of the world de- 
duced from the table of ratios would be 3,000,000 years. 
"^f our attempts to ascertain the age of the w^orld, or 
the duration of any single period of its evolution, yield 
only uncertain results, they suffice at least to demonstrate 
that geological history has limits far within the wild con- 
ceptions of a certain class of geologists. They show, if 
we may credit the indications here regarded most trust- 
worthy, a restriction of the modern epoch within limits 
not exceeding one-tenth or one-twentieth the duration 
sometimes assigned to it>* This conclusion, it may be 

*The author has long entertained and often expressed this view. It has 
also been recently expressed bj- Prof. H. Carvill Lewis in a lecture at the 
Franklin Institute, Jan. 5, 1883. Also b\' Prof. G. F. Wright, in a paper before 
the Boston Soc. N'at. Hist., March 7, 183S, noticed in Science, I, 269-71. 



THE MOON". 379 

mentioned incidentally, bears on the antiquity of the Medi- 
terranean race, since it is generally believed to have made 
its appearance during the later decline of the continental 
glaciers. It does not concern, however, the antiquity of 
the Black and Brown races, since there are numerous evi- 
dences of their existence in more southern regions, in 
times remotely pre-glacial. 

§2. THE MOON. 

II manque quelqne chose aux ge'olognes pour faire la geologic cle la Lune, 
c'est d'etre astronomes. A la verite il manque aussi queique chose aux astro- 
nomes pour aborder avec fruit cette etude, c'est d'etre geologues.— M. Fate. 

Die Anziehung welche die Erde an dem Monde ausiibt, zur Zeit seiner 
urspriinlichen Bildung, als seine Masse noch fliissig war, die Achsendrehung, die 
dieser Nebenplanet damals vermuthlich mit grosserer Geschwindigkeit gehabt 
haben mag, auf die angefiihrte Art bis zu diesem abgemessenen Ueberreste 
gebracht haben miisse.— Kant. 

1. Planet ological Retrospect, — The moon's volume is 
.0203; its density .6167; its mass .0125,* the earth's corre- 
sponding constants being unity. The relative amount of 
heat originally possessed by the moon must therefore have 
been .0125; but its relative rate of radiation was .07442. 
The relative duration of corresponding planetary periods 
was therefore .1679. That is, the moon cooled nearly six 
times as rapidly as the earth, and its present stage is six 
times as far advanced, if we regard only the rate of refrig- 
eration.! If the earth's incrustation began fourteen million 
years ago, and the moon's began at the same time, the 
moon reached the present terrestrial stage eleven and two- 
thirds millions of years since. The earth was only two- 

*0r, according to Newcomb, .012279. The density given above is calculated 
on the assumption that the moon is a sphere having a diameter equal to that 
of its visible disc. But in fact the visible disc presents the least two of three 
diameters; and hence the actual density of the moon is slightly less than the 
value given above. 

t From the formula in a note on p. 217, T = — ^.ijVWs = 1679 ; and .JF?^ = 



380 SPECIAL PLAJ^^ETOLOGY. 

thirds through its Pyrolithic ^Eon. In truth, however, 
according to our present reasoning, the moon reached its 
incrustive stage in one-sixth the time required by the 
earth, reckoning from the epoch when the moon separated 
as a distinct mass of fire-mist; and the lunar stage, corre- 
sponding to the present terrestrial, must have been reached 
much earlier in the Pyrolithic ^Eon, and perhaps even be- 
fore the earth's incrustation began. 

The earth was then another sun to the supposable 
inhabitants of the moon, having an apparent diameter 3|- 
times as great as the present sun — if we take no account 
of the earth's greater volume and the moon's less distance 
in remote epochs. Whatever the incrusted age of the 
world, the lunar stage corresponding to the earth's habit- 
able condition was coeval with the self-luminous eeons of 
our planet. By a simple calculation based on relative 
diameters and distances of the sun and earth from the 
moon, it appears that at equal temperatures the earth 
would supply the moon 124- times as much light and heat 
as the sun.* The temperature of the sun, however, was 
very much higher than that of the earth in the early 
incrustive stage; and the solar surface had probably not 
yet withdrawn to its present distance from the earth. 
. If the moon at that remote period had already attained 

♦Let El = the thermal force of a unit of surface on the earth. 
Si = the same on the sun. 
d = mean distance of the sun from the moon 
d' = mean distance of earth from moon. 
R = radius of sun, and ?' = radius of earth. 

e = number of units of radiating surface on tHe earth's hemisphere. 
s = same on the sun. 

Then E i = ^^ and e = ^f • 

Hence the thermal fprce of the earth's hemisphere is 

But Si s is the sun's thermal force, and calling this unity, we obtain 
di r2 _ (92,330,000)2 x (3959)2 _ 
~ d'2 R.' " (240,000)2 X (430,000)2 - ' "^ ■ 



THE MOON". 381 

to synchronistic axial and orbital motions (which, however, 
is improbable), it would result that one side was sub- 
jected to a constant radiation of heat from the earth, while 
at the oppositions, the same side received also the inces- 
sant heat of the sun. Simultaneously the apogeal side 
was turned from the influence of both bodies. Under 
such circumstances it is probable that all water resting on 
the heated hemisphere would be vaporized and a portion 
of the clouds, floating to the cold side, would be precipi- 
tated in fortnightly deluges of rain. During the next two 
weeks, the deluged side, through constant exposure to the 
solar heat, must have been scorched to such a degree that 
the atmosphere became burdened with clouds, and the 
satellite was completely wrapped in vapors, as I have to 
suggest may be the condition of Mercury at the present 
time. Even in our day, when the heat radiated from the 
earth must be nearly imperceptible, the constant exposure 
of one hemisphere of the moon to the sun's rays during 
two weeks, alternating with constant exclusion of solar 
heat during the next two weeks, may produce, as has been 
thought, a physical condition quite difficult to reason out. 
Lord Rosse calculated that the oscillation of temperature 
during a lunation must be as much as 500° Fahr. It is not 
impossible that the actual temperature fluctuates from 
two hundred degrees below zero to as much above; though 
Professor S. P. Langley's recent researches on the absorp- 
tive property of the terrestrial atmosphere, and the in- 
creased rate of radiation under diminished atmospheric 
pressure, reminds us that thermal vicissitudes on the 
moon's surface may not be as great as has been supposed.* 
The fact that no cloudy vapors are ever revealed on our 
satellite's surface is sufficient proof that in its present 
stage it is destitute of surface waters. The absence of all 
indications of water and an atmosphere is a circumstance 

* See this subject considered under the last head of this section. 



382 SPECIAL PLANETOLOGY 

which would not at first be expected on the basis of a 
theory which derives the moon from the mass of the earth. 
We must endeavor to explain it. 

M. Sasmann suggested, a few years ago,* that in the 
progress of cooling, the w^ater and the atmosphere may 
have entered into the pores of the lunar rocks; and on the 
basis of Durocher's experiments on the absorbent property 
of various minerals, he made a rough calculation which 
showed that the earth will eventually acquire sufficient 
porosity to absorb both the ocean and the air.f That the 
fluids of the moon have thus disappeared seems entirely 
reasonable on the ground of nebular theory; since, as I 
have shown, the moon's relative age is six times as ad- 
vanced as the earth's, while the progressive cooling of any 
planet constituted like the earth must deepen the zone 
of rocks sufficiently cooled to permit water to occupy its 
pores, and afterward to afford space for the entrance of 
the planet's entire atmosphere. | 

* Saemann, On the Unity of Geological Phenomena in the Solar System, 
Bull, de la Soc. ge'ol. de France, February 4, 1861 ; translated in Canadian 
Naturalist, vi, 444-51. 

t See this subject discussed hereafter in Part II, ch. iv. 

$ A general formula maybe readily deduced which, by the substitution of 
the requisite constants will apply to any planet. 
LetR = the radius of a planet: 

r = the radius of the sphere within the zone whose pores are capable of 
absorbing the water of the planet: 

i — the index of absorption by volume ; that is, the volume of water absorba- 
ble by a unit of volume of rock. 

W = the volume of water on the surface of the planet. 

w = the relative amount of water surface on the planet. 

d — mean depth of water beneath the water surface. 

Then, disregarding the thin superficial zone which may be already satu- 
rated with water, we shall have 













f.R3_4..3 = W 
3 3 i 


nee 










r3 - R3— 3W , 
4 ni 


since 


W = 


= 4 7rR2 


w d. 


we obtain by substitution, 




r-v'p.r-R-''""'^ 



THE MOON". 383 

2. Tidal Forces o?i the 3Ioo9i. — The tidal protuber- 
ance upon the moon must have presented, in all stages 
of its evolution, a comparatively enormous development; 
and its influence upon the moon's physical condition and 
aspects must have been permanently recorded. As the 
moon's relative mass is .0125, this fraction represents the 
moon's relative tide-producing power upon the earth. 
The tides on the moon must, therefore, have always pre- 
sented a development many times as great as the lunar 
tides on the earth. The problem of the linear height of 
the tide produced by the earth on the moon is quite diffi- 
cult of solution, but a few considerations will show the 
way to an approximate result. (1) The height of the geal 
tide on the moon must be a direct function of the relative 
mass of the earth. (2) It will be in the inverse ratio of the 
radii of the earth and moon, since we may here assume 
that the same tidal force acting on larger and smaller 

If r' = radius of the sphere within the zone capable of absorbing both water 
and air, 
A = volume of the atmosphere reduced to its density at the surface of the 

planet, and 
a = relative volume of the atmosphere, that of the planet being unity. 

Then inB^-^nr'^=^ + \ 

3 3 i 

And r'2 = R, 3R2^(Z 3 A 



i 4tn i 



But A = - TT R2 X a,. 



4 _ T?2 ./ „ . 3 A _ a R2 



3 47ri 



and substituting, 



'•'=fR^(R-iilll±^) 
lich the planetary crust is J 

-4/(k-d) —, 



If D = the depth to which the planetary crust is already saturated with 
water, then 



And '•'=y(R-D)' 



3 Ra w c? + a R 



in which T) = p {I' — t) -\- c, where p = rate of increase of temperature down- 
ward; that is, number of feet or other dimension to one degree of increase; 
c = depth from surface to constant temperature ; t = constant temperature at 
depth c, and t' — temperature at which water passes into steam. 



384 SPECIAL PLAI^ETOLOGY. 

bodies, with other conditions the same, produces prolate- 
ness of the same eccentricity in the two bodies. (3) 
Other things being the same, the height of the geal tide 
on the moon will be directly as the force of gravity on the 
earth or inversely as that on the moon. In other words, 
the geal tide on the moon will be about eighty times higher 
than the lunar tide on the earth in consequence of the 
earth's superior mass; and six times as high, in conse- 
quence of the moon's inferior gravity at its surface; and 
it will be one-fourth as high in consequence of the moon's 
smaller size.* The product of these factors gives, roughly 
speaking, a geal tide on the moon about 120 times as 
high as the lunar tide on the earth. 

I have already expressed the opinion that the deforma- 
tion of the solid or incrusted earth through lunar tidal 
influence, probably reveals its existence in increase of 
volcanic and seismic phenomena at the epoch of lunar 
syzygies, and perhaps even in nearly the whole amount of 
internal heat existing in the earth. From this point of 
view, volcanic and seismic phenomena must always have 
been many times more violent on the moon than on the 
earth. 

* That is, in general terms, t = T . ^ . — . ?. (see also general formula, 

m R g' 

p, 229), where M andm = the masses of two planets, 

T and f = the heights of the tides borne by them respectivel}', 

R and r = their radii, 

g and g' = the force of gravity on their surfaces respectively. 

Taking the values for the earth and moon from the Encyclopcedia Brit., 

— = 81.4. ~ = .2725 and ^, = — ^ = 6.043, 
w R g' .16547 

whence t = 134 T, 

This result is sufficiently in accord with a remark of M. Faye {Annuaire, 

1881, p. 721). '-La maree terrestre, comptee a partir du niveau moyen desmers, 

est de 0"'..37. La mare'e lunaire devait etre de 40'" et meme plus." Now |o 

= 108. M. Faye adds in a note. "Si Ton pouvait tenir compte de la faiblesse 

de la deusite' moyenne de la Lune, et de ses dimensions primitives, plus grandes 

alors qu^aujourd'hui, on trouverait probablement plus de 40'". "^ The method 

of calculation given in this note makes it .37™ X 134 = 49'". 58. If we take the 

relation given in the text it is .37'" X 120 = 44'". 4 

25 



THE MOON, 385 

3. Physical Aspects of the 'Moon. — To render intel- 
ligible any reasoning respecting the physical history of 
later stages of the moon, it is desirable to offer a few- 
explanations of the aspects of the lunar surface. To the 
unaided eye, the distribution of light and shade presents 
a configuration which, from the time of Plutarch, has been 
likened to the face of a man,* and which, by Helvetius, Was 
regarded as a water surface, the various divisions of which 
have, by later selenographers, been designated seas, lakes 
and bays. The unaided eye also discerns some regions of 
peculiar brightness, and even some radial arrangements of 
bright and dark lines, as well as indications of a very 
complicated detail of structure in all parts of the sur- 
face. By means of optical instruments all these features 
are brought into wonderful distinctness. The study and 
mapping of the moon's surface have been pursued by 
modern selenographers with great assiduity, so that at the 
present time we have maps and descriptions of all parts of 
the lunar disc as detailed and exact as of any region of 
the terrestrial surface. Professor J. F. Julius Schmidt 
completed, in 1874, a map of the moon, on which he had 
labored for thirty-five years, and on which he had laid 
down, as the result of exact triangulations, the altitudes 
of 3,000 mountains, the position and form of 250 hills, 
35,000 craters, and an immense number of minor features, f 
These studies, together with those of Lohrmann, Gruit- 
huisen. Beer and Maedler, Nasmyth, Neison and others, 
have given us lunar positions which, in the central parts 
of the moon's disc, cannot be in error over 3,000 feet, 
while the altitudes of the mountains are exact within 100 
feet. J Besides the results of triangulations, we possess 

* Phitarch : Be Facie in Orhe Lunce. 

t Vierteljahresschrift cler Astronomischen Gesellschaft, Leipzig, ix, 233-6. 

t"We liave a better map of the moon's surface," says Professor Lewis 
Boss, of the Dudley Observatory, "than of the State of New York "' {Reiiort 
New York State Survey for the year 1S77, p. 20) ; and this statement is true of 
the whole territory of the United States. 



386 



SPECIAL PLAXETOLOGY. 



the beautiful photographs of the moon, executed by 
Rutherford, de la Rue and Draper; and these show cer- 
tain features more distinctly than direct telescopic vision. 
Selenographers arrange the features of the moon's disc 
under three general heads, Plains, Craters and Mountains; 
but the last two desio-nations must be understood in a 




Fig. 54.— The Moon. 
[Telescopically inverted. Hence the top is south, the bottom north, the 
right hand east and the left hand west.] 

1. Tycho, 11. Mare Tranquillitatis, 

2. Copernicus, 

3. Kepler, 

4. Aristarchus, 

5. Theophilus, 

6. PtolemtBus, 

7. Bullialdus, 

8. Linne, 

9. Hyginus, 
10. Mare Serenitatis, 



12. 


'■ Foecunditatis, 


13. 


" Xectaris, 


14. 


" Crisium, 


15. ' 


" Frigoris, 


16. ' 


" Imbrium, 


17. ' 


" Xubium, 


18. ' 


■' Humorum, 



19, Oceanus Procellarum. 



special sense, and not as expressing any close analogy 
with terrestrial features. The plains occupy over half of 
the lunar disc. Most of them are dark and well defined. 



THE MOOIS'. 387 

while the remainder are light and undefined. The craters 
are divided into nine classes, and the mountains into 
twelve, but these numerous modifications need not be men- 
tioned here. 

In general character, all the principal craters, so-called, 
present a sub-circular form, surrounded by a rampart 
which slopes gently outwards, but descends precipitously 
on the inside to a depth considerably below the general 
level of the lunar surface. In the centre of the crater 
exist one or more mountain-like masses, which never rise, 
however, to the level of the surrounding rampart, and 
stand, generally in complete isolation from it. The verti- 
cal configuration of the crater will be better understood 
from the accompanying section through the crater Coper- 
nicus — more accurately styled a circle or walled plain. 



Fig. 55.— Skction Across the Crater Copernicus. 

The features here shown are of grand dimensions. The 
diameter is 56 miles, the crest of the crater 2,600 feet 
above the general surface, and 11,300 feet above the bot- 
tom of the crater. The bottom is, therefore, about 8,700 
feet below the general level. This depression of the 
interior is a uniform character of the craters or circles, 
and is especially marked in the smaller ones. The de- 
pressed bottom, moreover, as Sir John Herschel has 
remarked, is not a right plane, but presents a curvature 
conformable to that of the lunar surface, as if the matter 
had assumed form in a fluid state under the action of 
gravity. The central peak often rises to the height of 



388 



SPECIAL PLA>'ETOLOGT, 



ir 



IS" 







vy 



Fig 56.— Map of the C'RATFii Thfophilus and the Sukkouxding Region. 



From Neisou : Der Mond. 



THE MOOK. 389 

5,000 or 6,000 feet, but generally the central mass or 
masses is much less elevated. The surrounding rampart 
presents a succession of somewhat concentric, interrupted, 
terrace-like formations, as if produced by successive over- 
flows of lava which have subsequently been disrupted and 
eroded in deep valleys. These characters are well illus- 
trated in the accompanying map of the circle or crater 
Theophilus. This walled area is 64 miles in diameter, 
bounded by steep, lofty and variously terraced walls, 
which attain the remarkable elevations of 14,000, 16,000, 
17,000 and 18,000 feet, as if the mountain masses of 
Mont Blanc, the Jungfrau, the Matterhorn and Monte 
Rosa had been piled around the valley of Switzerland. 
The general crest of the rampart is 3,200 feet, or prob- 
ably higher, above the surface of the Mare Tranquillitatis. 
In the interior is a mountain cut by deep valleys into 
several separate masses, the highest of which is elevated 
6,400 feet above the floor. From the bounding wall 
extends a lofty ridge about 80 miles across the Mare Nec- 
taris. North of Theophilus stretches the Mare Tranquilli- 
tatis, which is diversified with numerous ridges and hill- 
ranges, radiating from Theophilus, and distinguished from 
the dark plain by their intenser light. 

Tycho is another walled plain or vast sunken amphi- 
theatre fifty-four miles in diameter. It is surrounded by 
a rampart sculptured in numerous terraces on the inner 
side, and which consists on the outer side of a mass of 
terraces and buttress walls, rising on the west 17,000 feet 
above the central floor, and on the east 16,000 feet, while 
the central mountain attains an elevation of 6,000 feet. 
The inner terraces are cut by deep gorges, and seem to 
bear some small craters. The outside of the rampart pre- 
sents an irregular structure, and assumes the aspect of a 
confused mass of mountains. The region more remote is 
crowded with mountains, walled plains and crater-like 



390 SPECIAL PLAXETOLOGT. 

depressions and pits — the last-mentioned in countless 
numbers. Tycho, like Copernicus and Kepler, is the cen- 
tre of a conspicuous system of light streaks radiating in 
all directions and spreading themselves over a fourth part 
of the moon's visible hemisphere. These cross indis- 
criminately all the other accidents of the surface — plains, 
craters, mountains and valleys. They are not seen best, 
like the other features of the disc, by oblique light, but 
are most distinct at full moon, and a few of the intensest 
can be distinguished when merely illuminated by light 
reflected from the earth. These bands are from ten to 
twenty miles wide, and stretch from 600 to 700 miles, 
while one of them crosses nearly the whole visible hemi- 
sphere of the moon — a distance of about 2,000 miles. 
The light of these streaks obscures many important struc- 
tures in the surrounding region. Similar light streaks, 
less extensively developed, radiate from Copernicus, Kep- 
ler, Byrgius, Aristarchus and Olbers, and, to a still smaller 
extent, from numerous other centres, especially between 
the equator and 13° north latitude. It is a curious fact 
that the distinctness of all these streaks is increased by 
photography. 

Besides these enormous walled areas, we find a multi- 
tude of smaller ones ranging down to a diameter of four 
or five miles; and also numerous still smaller formations 
of bright, circular outline, and steep, massive walls bound- 
ing depressions sometimes but half a mile in diameter. 
Finally, to this class belong also very numerous, small, 
isolated conical mountains or hills, from lialf a mile to two 
or three miles in diameter, having real crater-like pits in 
their summits. They occur on the crests of mountain 
masses, on the slopes of larger craters, on the ramparts 
encircling ringed areas, and in the bottoms of these sunken 
areas. 

One further class of structures requires mention. These 



THE MOON. 391 

are furrows or clefts in the surface — long, narrow, deep 
gorges or fissures, extending generally in right lines, 
sometimes branched or bent, and sometimes intersecting 
each other. They occur abundantly on the open plains 
without distinguishable beginning or end. They often 
pass through the middle of a mountain, or stretch from a 
crater into the surrounding plain. In other cases, they 
form a complicated net-work around some structure, or 
intersect the dejDressed floor of one of the larger crater 
forms. It is thought that not less than one thousand of 
these clefts have been laid down on the maps, and some of 
them attain a length of 200 to 300 miles. The two bound- 
ing walls are alike and generally rough, so that in some 
instances the cleft has the appearance of a chain of craters. 
The bottom of the cleft presents also a rugged aspect. 

The description of these voiceless lunar solitudes, with 
their weird and grandiose features, cannot but awaken 
interest and excite the imagination. The scene is a wil- 
derness of rocks and rents and pinnacled mountains and 
yawning pits. The sun rises on them slowly at the end of 
a fortnight of darkness, and his steady ray dispels the 
fierce cold of the departing wintry night. But no stir of 
conscious activity responds to day dawn, no bird of song 
rises on joyous wing to greet the rising sun. No murmur 
of a freshening breeze is heard among the tree tops, and 
no rippling rill prolongs its cheerful babbling down the 
rugged cleft in the mountain. The steady glare of sun- 
light warms the herbless and soilless surface, but no 
vapors rise to gather in a summer cloud. The wide area 
is lifeless, noiseless and motionless. This is the land of 
death. The mountains sleep in death, still lifting their 
dead and rigid forms to dizzy altitudes above the surface 
of a dead planet. The very pits sunken by thousands all 
over the convexity of the lunar world look like the col- 
lapsed sepulchres of a vast and neglected cemetery. The 



392 SPECIAL pla:n^etology. 

rocky ramparts which rise upon the borders are the monu- 
mental stones which mark the tombs of all the life which 
once dwelt upon a planet, and the thousand rifts in the 
solid floor commemorate the throes of the expiring w^orld 
itself. 

Yet possibly faint indications of change still manifest 
themselves in this planetary corse. But they are the 
changes of disintegration and decay. The prolonged and 
unclouded intensity of the solar rays succeeding the in- 
tense cold of the bi-weekly night would cause expansions 
and contractions of the rocky surfaces and rock-masses, 
which would impair their cohesion and weaken the sup- 
ports of cliffs and walls. Students of the moon have 
occasionally fancied that certain changes had been noted. 
The little crater Linne, in the eastern part of the Mare 
Serenitatis, has been an object of intense interest in con- 
sequence of apparent variations in its aspects. It was 
first indicated by Riccioli. Lohrmann reported it 4^ miles 
in diameter, very deep, and under all illuminations dis- 
tinctly visible. Miidler found it 6.4 miles in diameter. In 
1866 Schmidt announced that the crater had wholly dis- 
appeared, though he had previously observed it as having 
a diameter of seven miles, and a depth of at least 1000 
feet. Many observations were now made by others. In- 
stead of Linne a white spot was found in nearly the same 
place, as supposed. Soon Schmidt noticed a little moun- 
tain in the middle of it, and later, several observers noted 
a circular depression in it, about six miles in diameter, 
while Secchi reported a crater half a mil^ in diameter in 
the middle of the white spot. During 1867, a slight de- 
pression was reported by some observers, and a crater-like 
pit by more. It was set down as not over one and a half 
miles in diameter. Huggins made it two miles, and Buck- 
ingham, a little later, three miles, outside measure. Dur- 
ing 1868, the object was much studied, and it was generally 



THE MOOK. 393 

admitted to possess the appearance of a crater-like depres- 
sion having an outside diameter of about seven miles, w^ith 
a distance of three miles across from crest to crest, a depth 
of not over 500 feet, and a small central cavity less than 
half a mile in diameter. This general appearance has con- 
tinued to the present. 

The reality of these apparent changes has been much 
discussed. There are indications so strong, however, that 
different observers have not had their attention upon the 
same object, that a definite conclusion is unfortunately im- 
possible. " Changes have actually occurred," says Neison, 
"or the description by Lohrmann and Madler, as v^ell as 
Schmidt's first declaration, was erroneous, since so great 
a change could be ascribed neither to variations of libra- 
tion nor of illumination."* 

The double crater Messier may also be mentioned as 
one in which changes are by some believed to have taken 
place in the relative size of the two craters. 

Meantime another supposed change has been reported, f 
Hyginus is a deep crater 3.7 miles in diameter, intersected 
by a cleft 1,500 yards wide, running northeast 65 miles, 
and continuing southwest until its total length reaches 150 
miles. Hyginus and the region about had been many 
times mapped and described before 1877, and no crater 
had been noted in all the neighborhood. But Dr. H. J. 
Klein, in May, 1877, reported in the region north of 
Hyginus, a large dark crater without a surrounding wall, 
but full of shadows. In June, he announced a dark en- 
circling band which on the next day had disappeared. 
During some months following, the indications of a crater 
became more uncertain, and March 8, 1878, they had 

* Nelson: DerMondunddieBeschafenheitund Oestaltung seiner Oberfldche, 
p. 133. A German translation of an English work which seems to be out of 
print. 

+ Neison, Astronomical Register ^-Kvii^ Nos. 201-3, 213. Also, "Anhang "' of 
Der Mond, 417-40. 



394 SPECIAL PLAXETOLOGY. 

entirely disappeared. On the seventeenth, however, the 
crater was again distinctly visible. Since that date a 
multitude of observers have testified to its existence, and 
it now occupies a place, as Hyginus N, which a score of 
competent selenographers declare to have been destitute 
of any such form previously to the year 1877. In view of 
all the observations, Neison, who has systematically 
studied them, concludes that the observations made, 
especially during 1879, have rendered it probable, in the 
minds of most selenographers, " that finally, a real case of 
physical change upon the moon's surface has been practi- 
cally demonstrated." * 

Still more recently we receive reports of apparent 
changes in the crater Plato. Mr. A. Stanley Williams 
writes that of thirty-seven spots seen in the crater in 
1869-71, six were not seen in 1879-82; while seven not 
seen during the first period were seen in the second. The 
mean visibilities of most of the spots observed in both 
series agree very closely, but eight show a decided varia- 
tion in brilliancy. Among the light streaks in the crater 
some change was noted, particularly in one which was not 
seen at all during the first twelve months of the first 
period, and is now larger and brighter than others pre- 
viously observed.! 

Most of those who have admitted the reality of 
changes in the lunar craters have been inclined to ascribe 
them to a volcanic origin; but others have very reason- 
ably questioned the validity of such a conclusion. The 
only supposable cause for such changes is the disintegra- 
tion resulting from the extreme fluctuations of tempera- 
ture already referred to. J These might effect the levelling 
of crater walls, and the partial filling of the cavity, if of 

* Neison: Der Mond, 440. 

■[Science, i, 311, Apr. 20, 1883, from Obsei-v., March 1. 

:;: Proctor: The Moon, ^Q-'i. 



THE MOON. 395 

small dimensions; but it is difficult to conceive of changes 
thus originated as resulting in the obliteration and reap- 
pearance of the crater Linne, the variations in the relative 
diameters of the craters Messier, or the complete creation 
of the well defined crater Hyginus N. Much allovi^ance 
must be made for the changing aspects of lunar objects 
under different kinds of illumination, much for the influ- 
ence of the terrestrial atmosphere, and much for the vari- 
ous degrees of excellence in telescopes and the eyesight 
of observers. When all these deductions are made, per- 
haps the greatest actual changes noted will not be found 
to surpass the probable results of rock disintegration 
under extreme fluctuations of temperature. 

The facts thus cited concerning the topograpny of the 
moon, make it clear not only that the physical conditions 
of the surface of that planet differ extremely from those 
of the earth, but also that its evolution has pursued a 
widely different course. We are, perhaps, in a position 
to reason out with a fair degree of probability the vicissi- 
tudes of the moon's physical history. 

4. Tidal Evolution of the 3Ioon. — Adopting the 
theory that the moon parted from the earth as a ring of 
fire mist and aeriform matter, and underwent spheration 
in the manner heretofore described, it becomes eminently 
probable that its axial rotation was not, at first, coinci- 
dent with its orbital revolution. The tidal influence of 
the earth, however, caused the moon to assume the form 
of a prolate spheroid, having its longer axis directed con- 
stantly toward the earth, or very nearly so. But, as the 
moon, by hypothesis, presented different sides successively 
toward the earth, different portions of its substance suc- 
cessively underwent elevation into the tidal swell, and 
successively subsided at the ebb. Had the substance of 
the moon at this time been a perfect fluid, the tidal rise 
would have responded instantly to the terrestrial attrac- 



396 SPECIAL PLAXETOLOGY. 

tion, and the summit of the tidal swell would have been 
directed always exactly toward the earth. But, as the 
substance of the moon w^as not a perfect fluid, internal 
molecular resistances retarded the response to the earth's 
influence, and the tidal culmination was always a little 
behind the zenith position of the earth. In other words, 
the prolate axis formed a small posterior angle with the 
line joining the centres of the moon and the earth. The 
value of this angle, or the lagging of the geal tide, would 
be inversely as the fluidity of the moon's substance. The 
vertical dimension of the geal tide, notwithstanding its 
large absolute value, is so small compared with the diame- 
ter of the moon, and a fire-mist substance possesses so 
high a degree of internal mobility, that it is highly im- 
probable that the lagging of the geal tide amounted to 
any considerable influence toward the retardation of the 
moon's rotation. Nevertheless, it must have acted as a 
real retardative cause on the moon's rotary velocity, and 
all the more so when the volume of the moon was greater 
than at present, and its distance from the earth was less. 
In the course of time, according to our conception, the 
matter of the moon had cooled to the condition of a 
liquid globe. The tidal swell was now reduced in alti- 
tude, but the internal mobility of its parts was diminished. 
The angle of lagging was, therefore, considerably in- 
creased, and the tangential component * of the earth's 
attraction on the tidal protuberance operated more effec- 
tively as a retarding force. At the same time, any lack of 
homogeneousness in the density or viscosity of the parts 
would cause frictional resistances which, precisely on the 
principle of continental resistances to terrestrial tides, 
must have added something to the causes retarding the 
moon's rotation. Still, the geal tide was so small com- 

* The reader will recall the exposition in a previous section (Part II, chap. 

ii. § 6.) 



THE MOOK. 397 

pared with the mass and volume of the moon, that the 
primitive rotation of that body was very slowly dimin- 
ished. Had the moon suddenly become rigid, its prolate 
form would never have reduced its rotation to synchro- 
nism with its revolution, since if the prolate axis could be 
once moved far enough to make an angle a little exceed- 
ing 90°, with the line joining the moon and earth, the polar 
protuberances would induce as much accelerative action 
as retardative. But the moon was not rigid, and hence 
its nearest pole was continually in such position that the 
earth's attraction was continually retardative. During its 
liquid state, therefore, the rate of rotation must have 
been considerably diminished, though it is far from prob- 
able that the synchronistic stage was reached. 

At length followed the stage of incrustation. Great 
complication in the action and interaction of the forces 
now ensued. This is the chapter of lunar history whose 
records are preserved in the strange and impressive forms 
remaining upon the visible disc of our satellite. The 
presence of a forming crust did not prevent the continu- 
ance of the geal and solar tides. These continually inter- 
rupted the continuity of the growing film. As a con- 
sequence, the incipient crust became a floe of floating 
fragments perpetually grinding against each other, per- 
petually cemented by the freezing lava which rose in the 
chinks and spaces between, and perpetually disrupted and 
rearranged by the disturbances of the recurring tides.* 
But as soon as rigidity began to appear in a continuous 
crust, most important changes were introduced in the condi- 
tions of tidal action. The solid film yielded less readily 
than the liquid beneath. Its rigidity caused it also to yield 
to a less extent. From the first cause the angle of lagging 

*This conception of the inflnence of tides during the incrustive period of a 
planefs life has been expressed by me in Sketches of Creation^ 1870, p. 51, and 
in earlier publications. 



398 



SPECIAL PLAXETOLOGY. 




Tide Against the Crust. 



was greater in the crust than in the molten core. From 
the second cause the liquid pressed against the under side 
of the crust, tending to elevate it in a tide of the altitude 
due to the nature of the liquid. The liquid portion, for 
instance, tended to rise in a tidal swell to the height of A, 

Figure 57; but the more rigid 
crust rose onh^ to B, and the 
liquid was restrained beneath 
it, pressing against it. This 
pressure was very greatly aug- 
mented by the greater lagging 
of the crustal tide. The mode 
of action is illustrated by the 
adjoining figure, 58, where E, E, 
E shows the direction of the 
earth, A represents the summit 
Fig. 57. Action of the In ternal of the crustal tide, with a lag- 
ging angle A O C, and B rep- 
resents the summit 
A E ^f ^j^g J— J ^1^^ -f 

not restrained by 
-E the o V e r 1 yi n g 
crust, and having 
a smaller lagging 
angle, B O C. The 
portion of the 
liquid spheroid 
here shown exter- 
nal to the crustal 
spheroid is re- 
strained within the crustal spheroid, and consequently 
presses with all the force due to the earth's attraction 
against the under side of the crust. 

It would be impossible that the rocky lunar crust 
should attain, for a relatively long time, such soundness 




.J_^^ -E 



Fig. 58. Effect of Discordant Lagging Tides 



THE MOOia. 399 

and integrity as to resist fully the powerful tendency to 
rupture resulting* from tidal actions. The periodical press- 
ure exerted from beneath by the liquid tide would contrib- 
ute to this tendency. Fissures, perforations, chasms in 
the crust, would be certain to result. Through these the 
pent-up liquid would pour at high tide, in lava floods of 
frightful magnitude. With the ebbing of the liquid tide, 
the fluid lava would retreat. The apex of the crustal tide 
now arrived and the crust experienced a tendency to 
remain above the liquid core. Insufficient rigidity to 
stand the strain would prevent the development of any 
real cavity beneath, but the crust would float with dimin- 
ished pressure on the molten sea, and the fluid would be 
withdrawn from the openings. At the next tide of the 
liquid core, the matter would rise again through the vents 
and renew the vast overflow. Then it would again subside 
and the vacated perforations in the crust would become 
yawning pits illuminated by the glow of the lava sea re- 
vealed at bottom. These huge suspirations were con- 
tinued as long as a lava tide remained to gush through the 
outlets of its prison. Long-repeated overflows of molten 
matter built up around the outlets enormous rims of frozen 
lava. The craters attained frightful depths which were 
revealed when the lava tide was at ebb. Frequently, after 
the crater rims had become greatly thickened, the fresh 
outflow of liquid matter ran down the external slopes like 
watery floods, and eroded the older lavas in drainage 
gorges. Again and again^ the erosive action was re- 
peated, and the surrounding region for many miles pre- 
sented an aspect of vast and long continued denudation. 
Here were deep dark canyons winding to the lower levels; 
there were rugged bosses swelling above a sea of frozen 
lava; here were tower-like outliers of more ancient lava 
deposits which had escaped denudation, and there again, 
remained mountain masses of old lava, spreading their 



400 SPECIAL PLAIS^ETOLOGY. 

bases over many a square mile, and lifting their attenuated 
summits many a thousand feet above the surrounding 
region. 

It will be particularly noted that the vertical rise of the 
molten tide through the spiracles in the crust was not lim- 
ited to the tidal elevation proper to an open, unrestrained 
surface. The tidal pressure accumulated against the re- 
straining crust. The tidal swell, pressed back beneath 
the regions of unbroken crust, rushed with accumulated 
energy through the narrow vent when found. It was like 
the ten-fold tidal swell along the Hoogly or the Bay of 
Fundy. Hence it poured over the crater rims in torrents 
of astonishing depth. Hence, after the rims had been 
thickened to altitudes of thousands of feet, the rising flood 
could still attain their summits and lay down new deposits. 

Here also, are disclosed adequate causes of explosive 
action. Sometimes, when the pressure of the subjacent 
tide had greatly accumulated, the solid resistances sud- 
denly gave way. Fragments were thrown on high and 
columns of lava ascended probably hundreds of feet, as 
spouts of water rise at the end of a long " purgatory " on 
a rocky sea-coast, when the waves roll in and their gath- 
ered force spends itself in the free space above. These 
explosive occurrences must have scattered many huge 
fragments to great distances over the surrounding region; 
and, not impossibly, some of them were large enough to 
remain visible through terrestrial telescopes. The credi- 
bility of such occurrences is increased by the considera- 
tion that while the cohesive resistance of rock substances 
was the same as on the earth, and the force of rupture as 
great, the force of gravitation was only one-sixth as great 
as on the earth's surface.* 

♦ The moon's mass is to that of the earth as 0125 to uuity, and the relative 
attraction of this relative mass at the surface is inversely as the squares of the 
radii of the moon and the earth. Hence 



THE MOON. 401 

On our own planet there have been outflows of molten 
matter which spread themselves in fiery seas over tens of 
thousands of square miles. Tidal action, probably, had a 
connection with these events. On the moon, where tidal 
action was a hundred and twenty times as violent, the 
molten outflow must have sometimes covered extensive 
areas, and cooled into wide and level plains. The older 
rugosities would be evenly buried, and the aspect would 
be that of an ocean. Here and there some of the greater 
saliences caused in former times would project like Alpine 
" Grands Mulcts," or rocky islets, above the general level. 
Over the stiffening surface fell some of those projectiles 
hurled from the neighboring craters, and left their inden- 
tations on the pasty lava. 

If the moon was derived from the mass of the earth, 
the constituents of water and air must have belonged to 
it, and it is eminently probable that some portions of these 
elements were left to enter into those unions which form 
water and air. I cannot entertain the conception of an 
original destitution of those substances on our satellite. 
There must have arrived a time, therefore, as in the his- 
tory of the earth, when the condensation of aqueous va- 
pors took place. There must have been an aeonic storm. 
The rains must have fallen while the crust was still in- 
tensely heated. During this time the tidal swells and 
subsidences of the crust and molten interior were punctu- 
ally alternating with each other. The rains were descend- 
ing while the lavas were bursting through the crater 
vents. The rains descended on the lava seas. These me- 
teoric events enormously exacerbated the violence of the 
lunar activities. The cooling of the exposed molten sur- 
faces was accelerated, and the resistance to all movements 

which is. therefore, the moon's relative gravity, the influence of centrifugal 
force being neglected. 
26 



402 SPECIAL PLANETOLOGY. 

incident to tidal oscillations was correspondingly increased. 
Copious volumes of steam rose and condensed in clouds 
destined to perpetuate the storm and the reactions on the 
heated surface. The watery floods added their erosive 
work to that performed by the streams of lava. Both 
kinds of erosion ^vere enfeebled by the feeble intensity of 
gravity on the moon. 

But meantime, the crust was thickening, and the re- 
gions but little remote from the craters and the fresh lava 
streams, supported accumulations of water. The water 
was received in the pores of the rocks. In the progress of 
ages the crust was thickened to such an extent that ail 
the water belonging to the moon had been absorbed. 
With the entrance of water in the rocks a new explosive 
agent was in readiness whenever the confined lava tides 
burst through new fissures, or in rising through the old ones 
encountered watery infiltrations. The crust was now some 
hundreds of miles in thickness. The first 133 miles would 
take in all the water belonging to the moon, on the 
assumption that its whole volume bore the same ratio to 
the volume of the earth's water as the moon's volume 
bears to the earth, and that the absorbent capacity of its 
rocks was the same as that of terrestrial rocks.* It is 
manifest, therefore, that the continued thickening of the 
crust would increase its porous capacity to such an extent 
as to absorb all the lunar atmosphere. It is worthy of 
special mention that the thickening of the crust upon a 
planet undergoing such copious eruptions of molten mat- 
ter, would be more rapid than on a planet comparatively 
free from such eruptions. The increased rate of thick- 
ening would result both from the increased rate of general 
cooling, and from the addition of crustal layers upon the 
exterior. 

* This results from an application of the formula given on a preceding page. 
The method of determining the constants used will be shown when treating of 
the future stages of the earth. 



THE MOON. 403 

In the course of ages, the rigidity of the thickened 
crust became greatly increased. It yielded less to the 
tidal influence and the lagging angle was increased, and, 
therefore, the still fluid and tide-moved interior pressed 
with increased force against the under side. Perhaps 
many of the smaller vents had become sealed up in conse- 
quence of the permanent retention and final solidification 
of a portion of their lava contents, though the time had 
not yet arrived for solidification in the larger craters. 
Perhaps only the larger vents remained active; but their 
activity must have been somewhat enlarged. By and by 
the progressive reduction in the number of smaller vents 
resulted in a greatly increased pressure against the inte- 
rior. The thickness and rigidity of the crust rendered it 
impossible that the pressure should find relief in any new 
or reopened vents of small dimensions. The pressure was 
felt beneath areas a thousand miles in diameter. The 
whole solid crust yielded. It rose, uplifted by the strug- 
gling, imprisoned tide. There was a focus of tidal pres- 
sure determined partly by the position of the tidal apex, 
and partly by the place of relative weakness in the crust. 
Here the supposed lava burst through. The crust was 
shattered as by a blow from beneath. Long radial frac- 
tures diverged for hundreds of miles from the new-made 
vent, and these were filled by lavas which were modern in 
comparison with those which had been rent. The exist- 
ing accidents of the lunar surface sustained no perceptible 
ratio to the tremendous power which had burst a satellite. 
The fractures were rents in the general crust. They 
intersected older craters and mountains, as mere trifling 
incidents encountered in their course. After the cata- 
clysm was past, a vast system of radial dykes covered the 
district that had suffered. In later ages, the different 
color of the material, or the marked salience of the dykes 
after subsequent erosion, caused them to appear more 



404 SPECIAL PLAXETOLOGY. 

brightly illuminated than contiguous portions, when ex- 
posed to the solar light and viewed from the earth. Some- 
what such, perhaps, has been the history of those splendid 
star forms, Tycho, Copernicus, Kepler and others. 

Perhaps the numerous canals or clefts dej^icted on the 
map of the moon belong to the same period of lunar 
evolution. They bear an analogy, certainly, to the great 
vein fissures and trap dykes which intersect so numerously 
terrestrial formations in certain regions. We may con- 
ceive that similar causes originated them. They are con- 
nected with the progressive refrigeration of the planet, 
the contraction of its mass, the unequal strains resulting 
from unequal rigidity of different parts, and the repeated 
stresses created by tidal oscillations. 

While these great events were in progress, a powerful 
cause was in operation destroying the moon's axial rota- 
tion. Its action presented two modifications. First, the 
lagging of the tidal protuberance subjected it to the influ- 
ence of a horizontal component of the earth's attraction. 
The effect must be such as heretofore explained when 
ref erring- to the earth's diminished velocitv of rotation. 
Secondly, the retral pressure of the internal liquid tide 
against the under side of the crust, as illustrated in Figure 
57, was a more powerful cause of retardation. Finally, 
the period of rotation approximated the period of orbital 
revolution. The activity of physical work upon the moon 
was slackened. Longer intervals separated successive 
tides. The last overflows became more thoroughly chilled 
and torpid before new ones were poured^ over them. Now 
the pasty discharges rose slowly to the crater brim too 
viscid to leave readily the immediate border, and thus 
added the last courses to the grand rampart whose up- 
building had witnessed so many vicissitudes and so many 
revolutions. Probably the approximation to synchronism 
was gradual and continuous. Had the prolate moon been 



THE MOON. 405 

rigid and still destined to a synchronistic state, there 
would have been a time when the pole of the longer axis, 
after passing the point turned toward the earth, would 
have swung back and repassed that point on the other 
side. After a large number of oscillations, the exact 
position which it now has would have been finally as- 
sumed, and from that mean position it could never change. 
But the moon was not completely rigid, and hence the 
rotary motion was never reversed or oscillatory, and the 
synchronistic position was attained by progressive differen- 
tial retardation. 

The seon of lunar violence endured only while the 
moon's rotary period was unequal to its orbital period. 
If the moon, while yet in a fluid state, possessed a non- 
synchronistic rotation, as in all probability was the case, 
such rotation continued long after the precipitation of 
water upon the surface. The tidal swell, as I have main- 
tained, would not tend to retard rapidly the rotary velocity 
of a planet whose parts are entirely fluid. But if one 
part is rigid and another fluid, or if one part is less fluid 
than another, a relative translation of fluid parts must 
take place, and the friction of fluids and solids, or of more 
perfect fluids upon less perfect ones, under the influence 
of a tidally attractive body, would oppose that motion 
which determines local translation of the tidal wave. If 
the rotation is slower than the orbital motion, tidal fric- 
tion will accelerate it. If the rotation is faster, it will 
retard it. This relation of more and less rigid parts exists 
upon an incrusted planet having a molten interior; and 
such a condition supplied, probably, the principal cause of 
the final synchronistic relation of the moon's motions. 

If the moon, during the non-synchronistic £eon had 
acquired the condition of a perfectly rigid or nearly rigid 
body, and possessed at the same time a prolate form, with 
the matter symmetrically disposed about the centre of 



406 SPECIAL PLAXETOLOGY. 

gravity, such rigid prolateness, as I have stated, would not 
tend to retard the axial rotation, but the satellite would 
revolve indefinitely about its shorter axis. From this we 
infer that the moon is not a rigid body, or that its syn- 
chronistic motions became established before rigidity was 
attained, or that its parts were unsymmetrically disposed 
around the centre of gravity in pre-synchronistic times. 
But the moon has never been a nearly rigid body, since 
the earth is not rigid, and the moon is composed of the 
same materials in a lower state of condensation; and 
while unsynchronistically rotating, its parts must have 
been sjanmetrically disposed about the centre of gravity, 
since no reason can be assigned why they should be other- 
wise; and hence the establishment of the moon's syn- 
chronous motions was not effected through the influence 
of an eccentric axis, but by slow degrees through the 
action of parts tidally moved either upon or beneath the 
resisting crust. That oscillation or libration which La- 
place reasoned out was based on the supposition of a rigid 
globe, and it is not surprising, therefore, that even with 
modern observational precision, no librations have been 
discovered attributable to an actual oscillation of the 
prolate axis. 

If, after the synchronistic stage of the moon had been 
reached, any fluids free to move, like water or air, covered 
any considerable part of its surface, they would gather 
themselves on the farther side of the moon, since, though 
the centrifugal force is slightly greater on the opposite 
side, the difference in the earth's attraction on the near 
and remoter sides is about twice as great as the difference 
in centrifuo'al tendencies.* The arrano^ement of elements 

* The centrifugal force on the farther side is to that on the nearer side as 
1.00904 to nnity; but the earth's attraction on the nearer side is to that on the 
farther side as 1.01816 to unity. The difference in the terms of the ratio in the 
latter case is twice their difference in the former. 

It is worthy of note, however, that in the process of the lengthening of the 



'THE MOON. 407 

or parts free to move would, therefore, be determined by 
terrestrial gravity. This fact renders undemonstrable the 
conclusion that water and air are absent from the moon, 
since the opposite side might be covered by a sea 432 feet 
deep* in the middle without reaching to the visible hemi- 
sphere; and a corresponding atmosphere might rest upon 
its surface. But the complete absence of all refraction, 
and all spectroscopic change in the stellar or solar light 
passing close to the limb of the moon, tends to negative 
the supposition of water or air, since if they existed on 
the remoter hemisphere, air and aqueous vapor would 
occasionally reveal themselves upon the moon's limb, espe- 
cially at times when the lunar librations enable us to see 
beyond the limits of the mean hither hemisphere. It is, 
therefore, eminently safe to conclude, as we have, that the 
water and air of the moon have completely disappeared. f 

lunar revolution there was an epoch when the moon's distance was such that 
differential centrifugal force was just equal to differential attraction exerted by 
the earth. This, according to my calculation, was when the moon's angular 
velocity was 1.398 times its present angular velocity, which implies a period of 
19 days, 12 hours, 59 minutes and 29 seconds. At this epoch the fluids would 
have tended to distribute themselves equally around the satellite in spite of 
synchronistic motions. At a remoter epoch, with a still shorter revolution, the 
fluids would have tended to accumulate on the perig?al side. 

* Were the earth non- rotating (as the moon is practically) and covered by a 
fluid, its tidal semi-axis would exceed its shorter semi-axis 58 inches, under the 
moon's influence. Hence if the moon's apogeal hemisphere were covered with 
water, it would be maintained, making no allowance for tidal yielding of the 
moon's body at a depth approximately of 38K inches X 134 = 432 feet. This, 
strictly, is the height to which the geal tide would rise if the moon were cov- 
ered with water and the moon's body were a rigid sphere. 

It may be interesting to note that if the moon possesses no surface water, 
and its bodily rigidity is such that under geal tidal influence it yields one-half as 
much as a watery envelope would, tlicn the protuberance at each extremity 
of the prolate axis is 432 X H = 216 feet. 

tThe foregoing views respecting the tidal evolution of the moon were writ- 
ten out substantially as here given in March, 1S81. I had not then seen or heard 
of M. Faye's memoir on the geology of the moon, in the Anaualre for 1881, in 
which somewhat similar conceptions are set forth, and from which some cita- 
tions are made in the preseut exposition of my views. M. Faye, however, denies 
the former presence of water or air on the moon, and denies all analogy between 
the ancient activity of the moon and terrestrial volcanoes. 

According to the general theory here set forth, the crater phenomena of the 



408 SPECIAL PLAKETOLOGY. 

It would seem that lunar synchronous motions were 
attained while yet molten matter remained in the interior. 
The crater floors present the appearance of solidified lava 
pools. They conform to the general curvature of the 
moon's surface. But the thousands of feet to which we 
find these floors sunken, must bear a small ratio to the 
whole thickness which the crust had attained at the epoch 
of synchronism. Were the upper layer of the molten 
matter at any stage of the same density as the crust, the 
fluid would rise, in the case of a moon no longer tidally 
disturbed, to the general level of the lunar surface. If 
the fluid were lighter than the crust it would rise above 
this level; if it were heavier, it would come short of it. 
But the fluid was heavier than the crust, or the crust 
would have sunken. The depth of the lunar crater, there- 
fore, is determined by the excess of density of the molten 
matter over the density of the superincumbent crust. 
When we reflect that this excess was very slight, we can 
easily understand that a crater-bottom sunken 10,000 feet 
implies a total thickness for the crust many times as great. 

After the close of those tidal actions which wrought 
out the grand features of the moon's surface, there re- 
mained some concluding results of the long course of pro- 
gressive refrigeration. First, the subsequent lowering of 
the general temperature of the crust increased its density, 
and consequently its pressure on the subjacent fluid; the 
fluid as a consequence, sought to rise through openings in 
the crust, or to burst through the weaker places of the crust. 
There were few places so weak or so recently consolidated 
as the crater floors; and in these the thinnest and the least 

moon ought to be the most numerous in the region near the plane of the lunar 
orbit; but maps of the moon show them continuing with scarcely diminished 
frequency, quite to the vicinity of the selenographic poles. 

Further, on lunar craters, the reader may consult M. Bergeron, La Nature, 
1882, copied in Pop. Set. Monthly, xxii, 495-7. illus.. Feb., 1883; also H. J. Klein, 
Petef-mann's Mitlheilungen, translation in Observat07-y, and reproduced in Kaiv- 
BOS City Review, vi, 467, Dec. 1882. 



THE MOOX. 409 

supported parts were the central portions. Here, then, the 
residual fluid might most easily press through. Secondly, 
the same reduction of temperature resulted in contraction 
of the crust; and from this cause it pressed with increas- 
ing pressure upon the subjacent fluid. There was indeed, 
a time when the volume of that fluid was relatively large 
and its own abatement of temperature more than compen- 
sated for the increased constriction resulting from crustal 
contraction. But when the volume of fluid was greatly 
reduced and its protected situation caused much slower 
loss of heat, it seems probable that increase of crustal 
pressure would impel portions of the included fluid to 
seek chances of escape. Thirdly, the progressive thick- 
ening of the crust implies that liquid portions of lunar 
matter were continually becoming solid portions; that is, 
that some of the matter beneath the crust was becoming 
expanded and demanding more space. The action of these 
freshly solidifying portions upon the contiguous fluid 
furnished another source of pressure which made it neces- 
sary to seek relief. In these three causes, it seems to me, 
we have an explanation of those late exudations of lava 
which might have produced the central masses resting 
upon the floors of nearly all the lunar craters.* These have 

* Since this was written I have read for the first time some remarks bj^ Mr. 
W. Mattieu Williams, presented to the Royal Astronomical Society, March, 
1873, in a paper on The Origin of Lunar Volcanoes. He refers to the cooling of 
*'tap cinder "' from puddling furnaces, which is received in stout iron boxes or 
"cinder bogies/' "If a bogie filled with fused cinder is left undisturbed, a 
veritable spontaneous volcanic eruption takes place through some portion, gen- 
erally near (he centre, of the solid crust. In some cases this eruption is suffi- 
ciently violent to eject small spurts of molten cinder to a height equal to four 
or five diameters of the whole mass. The crust once broken, a regular crater is 
rapidly formed, and miniature streams of lava continue to pour from it; some- 
times slowly and regularly, occasionally with jerks and spurts due to the burst- 
ing of bubbles of gas. The accumulation of these lava streams forms a regular 
cone the height of which goes on increasing." The cii'cumstances under which 
these miniature cones are formed seem to be extremely analogous to those of 
the old crater holes on the moon after the attainment of the crustal quiescence 
due to the establishment of synchronistic motions. 



410 SPECIAL PLAXETOLOGY. 

been broken and dismembered by the movements attending 
the final stage of complete solidification of the satellite, 
as such final movements may also have fractured the cra- 
ter rims and opened the thousand rifts in the general sur- 
face. They have also been subjected to whatever erosive 
action may result from the extreme fluctuations of tem- 
perature supposed to be experienced on the lunar surface. 

These central monticles were therefore post-synchronis- 
tic, and the result of the last stages of lunar refrigeration. 
Since that epoch was reached, tidal and thermal forces 
being extinct, the lunar surface has presented only an 
unchanging scene of mighty desolations, oppressive still- 
ness and dead stagnation. 

5. The Atmospheric Factor in Lunar History. — On 
the ground of nebular theory, the moon in segregating 
from the earth, whether through annulation or rupture, 
must have received a portion of atmosphere or the ele- 
ments of such an envelope. As to the relative amount of 
atmosphere, we can scarcely make any other assumption 
than that its mass bore nearly the same ratio to the earth's 
present atmosphere as the moon's mass bears to the earth's. 
The mass of the lunar atmosphere would be one factor in 
the determination of its relative pressure on the lunar 
surface. The amount of surface on which it presses would 
be another factor. As the moon's surface is greater in 
comparison with the earth's than the moon's mass in com- 
parison with the earth's, this difference would diminish 
the relative pressure on each unit of lunar surface. The 
earth's mass is 80 times the moon's, but its surface is only 
13^ times the moon's. Aside from difference in atmos- 
pheric masses, pressure would be inversely as the areas of 
the moon and earth; or what is the same thing, inversely 
as the squares of the radii of the two bodies. Again, 
with equal atmospheric masses and equal planetary sur- 
faces, the relative intensity of gravity would be another 



THE MOOK. 411 

factor in determining the atmospheric pressure on a planet. 
When, therefore, we multiply together the ratio of the 
masses of the moon and earth, the inverse ratio of then- 
surfaces and the ratio of the intensities of gravity on the 
two bodies, w^e find the relative atmospheric pressure to be 
.02787 at the time when its normal proportion of the 
atmospheric medium was still present.* This result is 
somewhat surprising, and leads to interesting inferences. 
The barometric column stood at .836 of an inch, which 
implies an atmospheric pressure too insignificant to con- 
stitute a positive factor in a planet's genetic development; 
though it implies the virtual absence of those terrestrial 
actions which depend on the terrestrial atmosphere, and 
thus enables us to trace the divergence between the his-' 
tories of the two bodies. 

A barometric column of five-sixths of an inch corre- 
sponds to a terrestrial altitude of 17.7 miles, or over three 
times the height of the Himalayas.f Under such a pres- 

* We may embody these principles in a ger.eral formula. If M, S, R, g and 
P represent the mass, surface, mean radius, gravitational intensity and atmos- 
pheric pressure of the earth; and w, s, r, g' and;?, the same constants for any 
other planet, then 

w=P . ^* . 5 . ^' = p . 'Z^ . ^ . ^' :^ p . ? . ^' . ^', 
M s ' g M ' r-' ' (7 ' /• p g 

where p and p' represent planetary densities respectively. 

In the case of the moon ^ = .0125, -= 13.471 and ^'= .1655. 
M ' s g 

And i? = .02787 P. 

If we take the mean heiglit of the mercurial column as the measure of P, 

then the normal mean height of the barometer on the moon must have been 

h = 30 inches X .02787 = .836 inch. 

t The formula for the barometric calculation of heights in the latitude of 

Great Britain is 

h = log - X [60360 + (0—32°) (122.68)] (Maxwell : Theorrj of Heat, 222; see 

also, Deschanel: Natural Philosophy, Everett's ed., 164), where P and j9 are 

the pressures at the upper and lower stations, and h is the height in feet for a 

temperature t on Fahrenheit's scale. Here we may assume the temperature at 

32° Fahr. Hence the second term in the second factor reduces to zero and we 

have P 

h = log - X 60360. 

In the present case P = 30 inches and j^ — .836; hence 
h = 93.854.669 ft. = 17.77 miles. 



412 SPECIAL PLAKETOLOGY. 

sure the boiling point of water would be at 37^° Fahr.* — a 
result of extreme interest. The first inference to be de- 
duced from this atmospheric tenuity is the comparatively 
advanced stage of cooling attained before the precipita- 
tion of water began. The second is the very limited 
duration of the period of sedimentation, which would, 
indeed, be further slightly shortened by the commence- 
ment of ice-formation at a temperature above 32°. f 

The third inference is the low altitude at which the 
clouds must have been borne in so thin an atmosphere, 
since only the lightest cirrus clouds are borne by the ter- 
restrial atmosphere at an altitude of about eight miles, or 
one-half that required for the tenuity of the lunar atmos- 
'phere. In short, it may even be doubted whether vapor 
would be formed on the moon, even close to its surface, 
of sufficient density to cause rain. Not unlikely, the only 
precipitation was a cold fog resting on the surface of the 
planet. In this view, there was no erosion by waters, and 
no sedimentation; and the moon's water was absorbed 
simultaneously with the air. With a little further cooling 
of the planet, the lunar solidifying temperature of water 
was reached; and thereafter it was revealed in the liquid 
state only in situations when the sun's direct rays caused 
some elevation of temperature above the mean. A fourth 
inference from the existence of an atmosphere of such 
extreme tenuity, and holding so little vapor, concerns the 
influence of the sun's radiations on the lunar surface. It 
is well understood that the atmospheric and vaporous 

* By Sorefs formula (Deschanel: Xaf. Phil., Everett's ed., 338), 
A = 538 (212° — n, 
where t = the temperature on Fahrenheit's scale at which water boils at the 
height h in feet. Whence 

, = 2120- A. 

In the present case h = 93,854.669 ft., .'. t = 37^2° Fahr. 

+ See Maxwell: Theory of Heat, 176-7, and the authorities there cited. See 
also, this work, pp. 270-2. 



THE MOON". 413 

envelope of the earth absorbs a large percentage of the 
sun's thermal radiations, and partially restrains, also, the 
escape from the earth of such heat as succeeds in reaching 
it. The lunar condition here considered, therefore, admit- 
ted a higher intensity of solar heat, but at the same time, 
all situations with free radiation sent the heat back with 
correspondingly increased rapidity. The situation is' ap- 
proached when we ascend to the summit of a very high 
mountain. The sun's rays are, indeed, hotter, but the 
terrestrial radiation is augmented in still greater ratio, 
and the temperature is lower. Rising through the atmos- 
phere we remove successively some of the protective 
wrappings which keep the earth warm. Professor S. P. 
Langley has reported some observations made on the 
summit of Mount Whitney, a peak of the Sierra Nevada 
in southern California, attaining an altitude of 13,000 
feet. Here the solar rays heated to the boiling point 
some water in a copper kettle covered with two pieces of 
window glass to prevent radiation.* From these and 
other observations, it appears that our atmosphere at sea 
level absorbs about one-half of all the radiant solar energy 
— luminous, thermal and actinic — and that the selection 
of rays to undergo absorption is such that the white light 
reaching us, formed of the united rays of certain wave 
lengths, is not the color of the light resulting from the 
complete union of all the solar rays, but contains far too 
little of the blue and violet rays. Hence, Professor Lang- 
ley concludes, the color of the sun seen from a point 
beyond our atmosphere would be not only bluish, but 
positively blue. This, we must conclude, therefore, is the 

* S. p. Langley: The Mt. WhUney Expedition^ Nature, xxvi, 314-7. Further, 
on the " selective absorption" of the atmosphere, see his paper before the Brit- 
ish Association, 1882, in JS/ature, xxvi, 586-9, Oct. 13, 1882, republished in Amer. 
Jour. Sci., Ill, xxiv, 393-8; also a memoir in Ame)\ Jour. Sci., Ill, xxv, 169-96, 
March, 1883. Detailed results of the Mt. Whitney Expedition are to be published 
by the "U. S. Signal Service." 



414 SPECIAL PLAJs'ETOLOGT. 

color of the sun viewed from the moon, either after the 
complete absorption of its atmosphere, or even while 
retaining its normal atmosphere in such a state of tenuitv 
as has been indicated. In open space the rapidity of radi- 
ation, according to Professor Langley, must be so great 
that in spite of the intensity of the sun's rays, a sus- 
pended body would sink to a temperature below —50° 
Fahr. This, then, from this point of view, must be the 
upper limit of the surface temperature of the sunny side 
of the moon; and thus the fluctuations of temperature 
during a lunation must be vastly less than Lord Rosse and 
others have calculated; and the modern changes due to 
thermal fluctuations are diminished correspondingly. Dur- 
ing the whole lunar lifetime, even while the normal 
amount of atmosphere remained on the moon's surface, 
the temperature, after the formation of 'a cold crust, must 
have remained nearly at —50° Fahr. or below.* Not only 
water, therefore, but mercury and other substances known 
to us as liquids or gases, existed on the moon only as 
solids. In this view, the conception of aqueous erosion 
and sedimentation is entirely excluded, save so far as the 
primitive inherent heat of the satellite maintained at the 
surface a liquef3dng temperature. At the time when the 
residual effect of solar radiation, inherent heat and lunar 
radiation produced a surface temperature, say between 
34° and 37° Fahr., water may have rested on the lunar 
surface during the lunar da}^, but it would be consolidated 
during the lunar night. As some of this water occupied 
the pores of the rocks, here was a cause., of considerable 
disintegration, so long as the water had not sunken be- 
yond the reach of the thermal fluctuations. In any view, 

*This statement must be modified so far as the retention of the moon's 
water in the atmosphere would increase absorptive effects experienced by the 
sun's rays. The ratio of aqueous vapor to the whole atmosphere was much 
greater than the ratio of aqueous vapor in the terrestrial atmosphere, and rose to 
the ratio existing on our planet before primeval precipitation began. 



MARS. 415 

however, there seems little ground for inferring that the 
process of sedimentation was an important factor in any 
stage of lunar development. 

Thus, an attentive consideration of the divergences 
between lunar and terrestrial conditions reveals the inter- 
esting fact that lunar history must have presented charac- 
teristics widel}^ divergent from those of terrestrial history; 
and in this divergence, the tenuity of the moon's atmos- 
phere has performed a part quite comparable with the 
energetic work of the tides. 

§3. MARS. 

1. Phenomena of Mars and their Interpretation. — 
This planet has, in relation to the earth, a surface of 
.2828, a volume of .1470, a mass of .1108, a density of 
.7537 and an intensity of gravity at the surface of .3917. 
Its lower density may reasonably be attributed to its 
smaller mass. The length of planetary periods on Mars 
would be, according to the method of calculation pre- 
viously employed,* about two-fifths as great as on the 
earth. Hence, if the earth's incrustation began fourteen 
million years ago, Mars reached the earth's present condi- 
tion in less than five and a half million years after incrus- 
tation began. If Mars and the earth began incrustation 
at the same epoch, Mars had reached its habitable stage 
nine and a half million years ago, or at the beginning of 
Eozoic Time. This expresses the relative rates of evolu- 
tion of the two planets independently of any assumed nu- 

It will be noticed tiiat, as in the case of the moon, the same number expresses 
the relative length of the planetary period, and relative gravity at the planet's 
surface. This is because relative gravity varies as the mass and inversely as 
the square of the radius, and the relative length of the planetary periods 
varies as the mass and inversely as the surface; that is, as the mass and 
inversely as the square of the radius. These calculations take no account of 
centrifugal force on the several planets. 



416 SPECIAL PLAXETOLOGY. 

merical value of the earth's age, if we accept the table of 
time ratios previoush' given. 

According to our theory, Mars is an older planet than 
the earth; and for this reason, as well as its more rapid 
rate of senescence, it should be much further advanced in 
planetary life than the earth. The stage of atmospheric 
absorption, however, if we adopt the popular view, seems 
not yet to have been attained; and astronomers used to 
speak confidently of extensive watery areas on the surface. 
Moreover, we witness polar phenomena which seem to in- 
dicate alternate advance and retreat of the polar ice caps. 
On the whole the physical phenomena have been under- 
stood to indicate a planetary stage not very different from 
that attained by the earth. But we may doubt, not alone 
on theoretical grounds, but from the admitted fallacy of 
similar opinions formerly entertained concerning the 
moon, whether the diversified shades of color seen on Mars 
imply the real existence of surface water. An inspection 
of a map of Mars shows a distribution of light and dark 
shades which is very improbable, viewing them as areas of 
land and water. There are too many and too extensive 
long and slender arms of the sea, and these do not show 
any conformity to any fundamental planetary cause. The 
lonor-er axes tend rather to be transverse to the meridians 
than coincident with them. If the white areas about the 
poles are really snow-covered surfaces, as Sir William Her- 
schel first suggested, it might be inferred that the climates 
are quite comparable to those of the earth. The greater 
inclination of the planetary axis to tbe orbit, by the 
amount of 5°, would tend to diminish the extent of both 
polar ice caps.* Although the alternate advance and re- 
treat of these white areas, with the changes in the seasons, 
is confirmatory of the prevalent opinion respecting their 
natures, this must still be regarded a question under con- 

* Part II, ch. ii, § 9, 3. 



MARS. 417 

sideration. The ruddy color of Mars is generally ascribed 
to a dense atmosphere; but surely, if such an atmosphere 
existed, clouds of aqueous vapor must sometimes obscure 
some portions of the disc, and sometimes, indeed, the 
whole of it. In fact, the existence of polar snow implies 
the existence of clouds. These have never been noted, 
even in the polar regions of the planet. Father Secchi 
attributes a thin atmosphere to Mars and states that white 
spots are occasionally seen on his disc, which may be 
regarded as clouds, and that whirlwind movements may 
sometimes be seen in them.''^ Bat these statements in 
view of the results of calculations here adduced may well 
be distrusted. There is much reason, therefore, to doubt 
whether the popular interpretation of the visible phe- 
nomena of Mars is the correct one.f 

2. Tidal and Atmospheric Influences on Mars. — The 
tidal efficiency of the sun on the surface of Mars is ,4306 
relative to his tidal efficiency at the distance of the earth. 
The whole vertical fluctuation of the solar tide, therefore, 
on the surface of the water-covered planet would be four- 
teen inches, assuming that the conditions are otherwise 
such as enable the moon to cause upon the earth a tidal 
fluctuation of fifty-eight inches. | The tidal influence of 

* Secchi : Le Soleil, ii, 392. 

tProf. Elias Loomis, nearly thirty years ago, advanced the opinion that the 
equatorial region of Mars must have a mean temperature at 11° Fahr. below 
zero, and the poles, 51° below zero, and raises the question how the Martial 
snow caps could ever diminish under such temperatures. (Loomis, Proc. 
Amer. Assoc, 1855, 74-80.) 

t Employing the notation used when treating of the moon (p. 384), and 
denoting by / the sun's tidal efficiency at the earth and by /' its efficiency at a 
difEerent distance, the general formula becomes 

/ = T - /' - ^ 

But the tide-producing body being the same in the two cases here compared, 

- = 1. Also, here, ^ = .4306, ^ = ^,U and ^ =. |i|i, whence t = .6122 T; 

and when T = 58 X | = 23.2 inches, 

i = 23.2 X .6122 = 14.2 inches. 
27 



418 SPECIAL PLAXETOLOGY. 

the earth upon Mars is entirely insignificant, not amount- 
ing*, at the perigee of Mars, to a total fluctuation of more 
than one four-hundredth of an inch. The satellites of 
Mars, though in proximity sufficiently close to acquire 
marked tidal efficiency, possess too little mass to exert 
any important influence. The inner satellite, Phobos, if 
having a diameter of twenty-five miles, a distance of G,000 
miles from the centre of its primary, and a density equal 
to that of the primary (which is probably too great), 
would cause upon the ocean-covered surface of the planet 
a total linear tidal fluctuation of onl}- ten and a quarter 
inches according to my calculation.* The evolution of 

*It will be best, with a view to future applications, to deduce a rough gen- 
eral formula for the linear value of the tidal fluctuation on any tide-bearer, pro- 
duced by any tide-mover. 

1. Symbols referring to tide-bearer. 

Let T = fluctuation of tide on the earth produced by its tide-mover, 
D = distance of the earth's tide-mover, 
K = radius of the earth, 
"M = mass of the earth, 

g = intensity of gravity on the earth. 

t = fluctuation of tide on any other tide-bearer. 

d = distance of the other tide-bearer from its tide-mover, 

r = radius of the other tide -bearer, 
w = mass of the other tide-bearer, 

g'= intensit}' of gravitj^ on this tide-bearer. 

2. Symbols referring to tide-momr. 
7n'= mass of tide-mover acting on the earth, 

/x = mass of the other tide-mover. 

where —r: — tidal eificiencv depending on distance, 
a-* 

—^ = effect depending on mass of tide-mover, 

»' 
= effect depending on radius of tide-bearer, 

- effect depending on intensity of gravity. 



K 

m K2 



But g'— g . ^ --, and by substitution, 

■ di ' Rs ■ m 



MAKS. 419 

Mars, therefore, has proceeded without any considerable 
interposition of tidal forces. 

Supposing, as I have done in the case of the moon, 
that the Martial atmosphere bore the same ratio to the 
mass of the planet as the earth's atmosphere to the earth's 
mass, the density of the planet's atmosphere would be 
.138 relative to the earth's atmospheric pressure. This 
corresponds to a barometric altitude of 4.14 inches.* 
Hence the atmospheric pressure on Mars would be only 
such as our atmosphere possesses at an altitude of 9.88 
miles above sea level. f This result discloses at once a 
wide contrast between the surface condition of Mars and 
that of the earth, even during the period while Mars 
retained its normal amount of atmosphere. The thermal 
effect of the sun's rays would be greatly diminished; and, 
when we reflect that the sun's mean intensity at the dis- 
tance of Mars is less than half that at the earth, it be- 
comes apparent that the temperature at all seasons must 
be considerably below that of the earth. With the atmos- 
pheric pressure so low, we find that water would boil at 
the temperature of about 115° Fahr.:{: Hence precipita- 

This formula Is identiccal with that dediiced from the general expression for 
a tide (p. 229), but the rationale is here made more intelligible. 

In the present case. If .we make comparison with the fluctuation of the lunar 

tide on the earth, T = 58 inches; ?-? = ^^^^ = 64000: ^^ = (.5503)3; - ^ 

1 ^_ _ (25) 3 X .700 
.1081' m' " (2160)3 X .607' 

And t — 10.24 inches. 
* Using the formula given in the discussion on the moon, we have 

^" = . 108, 5^ = 111^, and ?^ = . 887, 
M s (2181)^ g 

Whence p = .138 P. 

If we take the measure of P as the mean height of the mercurial barometer, 

p = 30 in. X .138 = 4.14 inches. 

t Using, as before, the formula for barometric measurement of altitudes, 

h = log. ~ X 60360 = 51,916.9 ft. :^ 9.83 miles. 
4.14 

:J:From Sorefs formula, as before, 

OOO 



420 SPECIAL PLAXETOLOGY. 

tion and sedimentation did not begin on this planet until 
cooling had advanced a hundred degrees further than on 
the earth. As solidification of water, under diminished 
atmospheric pressure, took place at a slightly higher tem- 
perature than on the earth, the range of temperature 
within which denudation and sedimentation could have 
been carried on was greatly contracted. The attenuated 
atmosphere also promoted escape of heat from the planet. 
These considerations all point to a more rapid attainment 
to successive planetary stages, and lead definitely to the 
conclusion, indicated on other grounds, that Mars is not 
lingering in the terrestrial stage, but has lost all water 
and atmosphere, and advanced far toward the lunar stage 
of total refrigeration. 

§ 4. YEXUS AXD MERCURY. 

1. Venus. — Next to Mars, Venus is generally supposed 
to sustain closest planetary relations to the earth. Its 
diameter is .9475; its volume, .855; mass, .875; density, 
1.03, and the intensity of gravity at the surface, .982, the 
earth's correspondmg values being unity. The relative 
intensity of solar radiations at Venus is 1.913, or nearly 
twice that at the earth's distance. The relative length 
of the planetogenetic periods, according to principles 
previously explained, is .977. Solar tidal efficiency is 
2.613, and the relative linear height of the solar tide is 
2.543, which, on a water-covered planet, implies a total 
fluctuation of 7.37 feet. The pressure of the atmosphere, 
calculated from ratio of mass and surface, is .9595, which 
corresjDonds to a mean barometric height of 29.78 inches, an 
elevation on the earth of 192.91 feet above sea level, and 
a boiling point of 211°. 64 Fahr. In every particular, there- 
fore, Venus reproduces nearly the conditions of the earth, 
except those which arise from greater proximity to the 



VENUS AND MERCURY. 421 

sun — intensity of heat, light and tidal action, and these 
are not very widely different. We may therefore suppose 
a planetary history not far divergent from that of the 
earth. The surface of Venus is stated by some observers 
to be densely veiled in clouds. 

The nebular theory implies an increasing density tov^^ard 
the centre of the nebula, not only in consequence of in- 
ternal pressure, but probably through the gravitation of 
the denser constituents of the nebular mass toward the 
centre. The first cause would not operate after the sepa- 
ration of the planetary mass. Density due to superincum- 
bent pressure would now depend on the radius of the 
planet and the coefficient of condensation of the material 
under pressure. As Venus has a shorter radius and higher 
density, there is manifestly a certain amount of density 
due to the fact that the proportion of denser materials is 
somewhat greater in Venus than in the earth,* and this is 
as it should be. This subject, however, is connected with 
what follows. 

The excess of solar heat upon Venus must have exerted 
some influence upon the evolution of the planet. The 
rate of cooling was somewhat impeded, and this effect was 
relatively greatest in the later and cooler stages. After 
the epoch of aqueous precipitation, the solar heat efficiently 
reinforced the inherent heat of the planet in promoting 
copious evaporation and cloud formation. When the in- 
herent heat had so diminished that its surface influence 
became similar to that of the earth in historic times, the 
excessive heat of the sun still maintained a copiousness of 
evaporation double that upon the earth. As long as this 
rate of evaporation could be maintained, there must have 

* If the condensation of solids were proportional to pressure, as in gases, 
the density in this case would be .9519, and the excess of the actual density would 
be .078. But the condensation in solids is in a lower ratio than the pressure, and 
this excess is too great. 



422 SPECIAL PLAN^ETOLOGY. 

been also, a double amount of precipitation. But the 
effect reacted on the cause. The clouds formed prevented 
the free access of heat to the planet, and the amount of 
cloud formation and consequent precipitation was propor- 
tionally diminished. The final adjustment of these causes 
and effects determined a ratio of cloudiness and precipita- 
tion much greater than on the earth, but somewhat less 
than twice as great. Meantime the cloudy envelope of 
the planet must be nearly complete and permanent. I 
know of no ground for negativing the assumption that the 
vaporous veil which protects Venus is of such density as 
to admit about the same amount of heat and light as is 
received by the earth. The conditions on the planet's sur- 
face may easily be analogous to those upon the earth on a 
thinly clouded day. But while the cloudy envelope screens 
out solar heat to the terrestrial standard, it restrains, also, 
the process of radiation from the planet. Consequently 
the depression of temperature during the night is relatively 
less. Further, supposing the axis inclined toward the 
plane of the orbit, seasonal periods mark the year. But, 
in the winter season, the diminution of the sun's Intensity 
simply clears the atmosphere to a corresponding extent. 
The winter season is therefore the season of clearest skies. 
If Venus is surrounded by a perpetual mantle of clouds, 
astronomers have never seen the body of the planet. Its 
diameter is therefore less and its density greater than have 
been calculated; and we have so far confirmation of our 
deductive conclusion that Venus possesses a greater pro- 
portion than the earth of the heavier substances of the 
primeval nebula. In this view also, the diameter of the 
planet is not accessible to measurement; and the deter- 
mination of the rotary period will not be accomplished. 
There might be produced a belted arrangement of lighter 
and darker clouds in the equatorial region; but no fixed 



YEXUS AJ^D MERCURY. 423 

feature is likely to afford the means of ascertaining the 
length of the day.* 

2. Mercury. — Passing to Mercury^ we find a planet 
whose relative diameter is .3858; surface, .1489; volume, 
.0574; mass, .065; density, 1,12; solar intensity at peri- 
helion, 10.58; at aphelion, 4.59, with a mean of 7.58. f 
Its relative intensity of gravity is .432, which is only equal 
to that exerted by the earth at the elevation of 2,066 
miles above its surface. The relative length of the plane- 
tary periods, is therefore, .4366; mean solar tidal efficiency 
is 17.24, and the mean linear fluctuation of the solar tide 
in an oceanic envelope would be 15.41 or 29.79 feet. At 
perihelion the solar tidal efficiency is 34.39, and the rela- 
tive linear fluctuation in an oceanic envelope is 31.71, 
which implies an actual fluctuation of 66.49 feet. This 
tidal influence is experienced every 88 days. The tidal in- 
fluence of Venus, when nearest Mercury, compared with 
the lunar tide on the earth, would be only .000068, or 
about four thousandths of an inch. The pressure of the 
atmosphere should be .1882, corresponding to a barometric 
height of 5.646 inches. | This pressure is attained on 
the earth at an elevation of 8.29 miles, and implies a boil- 
ing point for water of 130°. 8 Fahr. As Mercury's per- 
centage of atmosphere is probably less than the earth's, § 
the results just given are probably too large. Mercury, 
therefore, differs from the earth to a very marked extent, 
not only in those points connected with greater nearness 

* Cassini. guided by certain supposed spots, calculated the rotation period as 
a little less than twenty- four hours. Schroter, by observations along the "ter- 
minator," believed that he had fixed the period of rotation at .973 d. This 
method implies the existence of high mountains on the planet. 

tThe orbit of Mercury has an eccentricity thirty tini66 that of Venus and 
twelve times that of the earih. 

X Mr. W. Mattieu Williams makes it four and one-fourth inches, but his method 
of calculation is not indicated.— Cwr/en.^ Discussions in Science, Humboldt 
Library, No. 41, p. 20. 

§ Mercury has sometimes been represented by observers as covered by a 
dense atmosphere loaded with clouds. 



424 SPECIAL PLANETOLOGT. 

to the sun, but also in everything connected with smaller 
mass. 

We have here a further and much more decisive exem- 
plification of the theoretical principle that heavier matter 
accumulated about the centre of the primitive nebula, 
since, while Mercury's diameter is only three-eighths as 
great as the earth's, its density is nine-eighths as great. 
Aside from the influence of solar heat in retarding Mer- 
cur\"'s developmental progress, we might probably regard 
this planet as advanced to a habitable stage. 

In consequence of the powerful tidal action exerted, 
Mercury must have undergone an incrustive history some- 
what analogous to that of the moon, but very much less 
violent. Aside from any consideration of the presence of 
water, it seems likely that its surface was powerfully 
marked by crater formations and an extensive system of 
fractures. But water was present, though probably in 
less proportion than on the earth, and some erosion and 
sedimentation have taken place, if we can admit the solar 
heat moderate enough to allow aqueous precipitation. 
During the day, with the solar intensity from 4|- to 10-|- 
times that experienced by us, it is scarcely credible that 
rain should fall except in situations protected by vapors. 
These would exist even during the day, and most copi- 
ously in the perihelion period; for in spite of the sun's 
intensity upon the exposed surface of the clouds, the 
rapidity of radiation would probably preserve a tempera- 
ture low enough for condensation. During the night, 
however, condensation would be vastly niDre copious, and 
hence the night side of the planet would be deeply veiled, 
and also deluged with rain. A violent thunder storm fol- 
lowed sunset around the planet continually. Thus all sides 
of the planet were enveloped in cloudy vapors, hovering, 
however, close to the surface. This condition of things 
began when the inherent heat had sufficiently abated to 



JUPITER. 425 

permit a temperature of 131°. I know of no advanced 
condition which should prevent its continuance to the 
present epoch. The powerful tidal action experienced by 
Mercury has greatly retarded its primitive axial motion, 
and increased its distance from the sun. No surprise 
would be occasioned by the proof that the planet has 
already attained to synchronistic motions. Its retirement 
from the sun has been accompanied by a growing infre- 
quency of perihelion positions and a diminishing intensity 
of all. the solar influences. 

Mercury, therefore, as well as Venus, is screened from 
telescopic observation, and nothing can be known of its 
actual diameter or period of rotation.* Owing, however, 
to the thinness of its atmosphere, and the low altitude of 
the clouds, the real density of the planet cannot be much 
greater than has been calculated. 

§5. JUPITER. 

1. Physical Relations. — This planet, in consequence of 
its enormous mass, presents physical conditions immensely 
different from those of the earth. Compared with the 
earth, Jupiter has a diameter of 11.06; a surface of 117.9; 
a volume of 1279.412; a mass of 308.990; a density of 
.242; a force of gravity at the equator, making allowance 
for centrifugal effect, of 2,254.t As the rotation period 
is 9 hours 55 minutes and 34 seconds, the equatorial cen- 
trifugal force is 63.13 times as great as on the earth, and 

* Schroter's observation, giving a day of twenty-four hours, five minutes, lias 
not been confirmed by other astronomers using far superior instruments. 

t These data are taken from the Annuaire du Bureau des Longitudes, 1881. 
They differ somewhat from those given in the Encyclopctidia Britatmica ; and 
both differ somewhat from Newcomb's tables in his Popular Astronomy. It 
will be found that the results of calculations in this chapter are in some cases 
inharmonious with each other, in consequence of employing data in different 
cases from different authorities. 



426 SPECIAL PLAXETOLOGT. 

diminishes materially the effective force of gravity.* Dis- 
regarding the effects of rotation, the relative surface 
gravity of Jupiter is 2.619.t This is therefore the force 
of gravity at the poles, neglecting the effect of oblateness. 
In any other latitude the actual intensity of gravity is 
given by diminishing the stationary gravity by the vertical 
component of the centrifugal force in that latitude. The 
centrifugal force at the earth's equator is equivalent to 
0.1112 feet per second, J and that on the equator of Jupiter 

* Letting ?■,/, t and v represent the mean radius, equatorial cenlrifugal force, 
rotation period and equatorial velocity of Jupiter, and R, F, T and V the same 

in respect to the earth, we have by a familiar dynamical principle F = ^ 

and/ = ^ . Therefore Y : f :: ^ -. ^ and / = F^ • ^. But t> : V :: ^ : ^ .-. 

vi T2 ?'2 T2 r 

V^ "^ T' ■ R' • ^"*^' substituting, /= F • — = ^. By putting T = 86,164 seconds, 

t = 35,720 seconds, R = 3959 miles, r = 43,000 miles and F= 1, we obtain/ = 63.13. 
The vertical component of the centrifugal force in any latitude A., is therefore 
/^ = 68.13 cos2 A, and for the latitude of 45°, /'= 31.57, 

t Since surface gravity is directly as the mass and inversely as the square of 

the radius, we have, adopting notation similar to the last, g' = g — • —~ = 2.619. 

Taking the oblateness of Jupiter as rr-^' and the mean diameter as 84,843 

lb. 88 

(Encyc. Brit.), equatorial gravity is reduced to .9601 of the gravity computed on 
the assumption of a spherical planet, This reduces the force of gravity on 
Jupiter's equator to 2.619 X .9601 =2.515. For, if D and d represent the trans- 
verse and conjugate diameters of the oblate spheroid, and ?•, the radius of the 
equivalent sphere, 

1 77 r3 = ^77 D-2 rf ; whence D2 x ^Jl. 
d 

But, as ^^-^ = -^^, d = j^^, and substituting, 

D3 = 8.504 7-3, and D = 2.041 r = 86,590 miles ; 

8 t'i 
whence d = ^ = 81,460, and I> — d = 5130 miles. 

Finally, if g' and g" represent equatorial gravity on the'- sphere and spheroid, 
rf ?-2 4 X (42,421.5)2 



I4 U2 (86,590)2 



.9601 as above. 



i The equations F = :„- and V= — =— give us F = — =^y- • 

Whence, taking the mean radius of the earth at 29,923,900 feet, according to Sir 
John Herschel, F = .1112 feet per second. Whence the equatorial centrifugal 
force on Jupiter is .1112 X 63.13 = 7.025. Or, we may obtain this result from the 
independent formula, 

4 7r2 7' 4 7r2 X 43.000 ^ „. 
^=-W-^ (35720)2 ='-Q^5- 



JUPITER. 427 

is 63.13 times as much, or 7.02 feet. As the space through 
which a body falls in a given time is proportional to 
gravity, a body falling 16.15G7 feet in one second on the 
earth's equator, making no allowance for centrifugal force, 
or 16.0455 under the actual centrifugal force, would fall, 
on Jupiter's equator, 42.3 feet, making no allowance for 
centrifugal force, or 35.3 feet under the actual centrifugal 
force on that planet. 

When we attempt to reach some conception of the 
relative length of planetary periods on Jupiter, it becomes 
apparent that the great present disparity of densities 
renders it necessary to reduce Jupiter to the earth's den- 
sity, or to reduce the earth to Jupiter's density. Now, if 
Jupiter had the density of the earth, his mean diameter 
would be 53,530 miles;* his relative surface, 45.7, and the 
relative length of his geological periods, 6.761 times the 
length of the corresponding periods on the earth. f If, on 
the contrary, the earth were reduced to the density of 
Jupiter, its diameter would be 12,721 miles and its surface 
-:^\ that of Jupiter, or 2.581 times its present surface.]; 

* Employingnotation as before. ;ri: = -j^, clensitie& being the same. Hence 



'' M ^ 1 

t Employing the same principle as heretofore, 

s 45.7 
X Since on this snppoeition — = ,^^1 

^ - V -^ = V ---mm- ^ ^■^'^■'' "^^'^^- 

Further, tlie earth's relative surface on this supposition would be 

and since = 45.T, this number represents Jupiter's surface relatively to the 

earth when reduced to Jupiter's density. 

Also, S'= ^ 

times the earth's present surface. 



-=^-^=^^ir-- 



428 SPECIAL PLAXETOLOGY. 

Ill this case the surface of Jupiter, in relation to that of 
the earth, would be 45.7. as before, and the relative dura- 
tion of his planetary periods would be 6.761, as before.* 
But basing a calculation on Jupiter's actual volume, as 
ordinarily stated, we find the relative length of his planet- 
ary periods to be 2.62. Some idea of the relative energy 
of ^ meteorological forces on this planet ma}' be had by 
recalling the fact that the velocity of the trades and anti- 
trades is determined by the velocity of a point on the 
planet's equator. In Jupiter, we have a planet rotating 
2.4 times as rapidly as the earth, with a radius 11 times 
as great. Hence, a point on his equator moves more than 
26 times as rapidly as a point on the terrestrial equator; 
and other things being the same, the Jovian trades and 
anti-trades should move with a terrific velocity. Their 
effects, moreover, would be increased six-fold by the supe- 
rior density of Jupiter's atmosphere. But other things 
are not the same, since the solar heat at the distance of 

* Jupiter's actual surface in relation to the earth's actual surface is 117.9. 

The earth's surface, if having the density of Jupiter, would be. in relation to the 

present surface, 2.5SI : and hence Jupiter's actual surface in relation to the 

117 9 
earth's, if having Jupiter's density, would be — :^^ = 45.7,— the same ratio as 

when Jupiter is supposed reduced to the earth's density. It may be readily 

shown that this is as it should be, for. 

Let S and s represent the surfaces of the earth and Jupiter, 

S' and s' their surfaces respectively, when each is reduced to the other's 

density, 
R and r their actual radii, and R' and r' their radii respectively, when re- 
duced each to the other's density; 

Then, s' = S.^, = ~ when S = 1 : and s = S.£ ^ S.^, = ^- 

K- IX- xx- xt- Iv - 

Now, if o- and o-' represent Jupiter's two supposed densities, and p and p' the 
earth's, and v, v', V and V be employed similarly for volumes of Jupiter and the 
earth, wc have 

-^ ^ !i' = ^: .•.r'3=r3.^„and^ = ^= ^; .-.Wi^mA, 
a' V /-i <t' p' V R;^ p' 

2. R2 

But 0-' = p = 1, and p' = <t\ .-. 7''-' = r^ p' 3 , and R'-^ = —^. 

p'S 

Hence, by substituting s' = "^ /^ , and s = "„ - : •"• s' = s. 



JUPITER. 429 

Jupiter is only ^ly the intensity experienced at the earth — 
taking no account of the warming influence of the supe- 
rior density of the atmosphere. As solar heat is the 
cause of the atmospheric circulation, it appears that the 
velocity of the Jovian trades must be about the same as 
that of the terrestrial trades, if the Jovian atmosphere is 
of the same depth. But the solar thermal disturbance of 
equilibrium being less, the velocity of the movement due 
to this is less: the velocity to and from the equator is less 
rapid, and for this reason, combined with the superior 
rotary velocity of the planet, the resultant movement 
across the meridians approaches much more nearly a right 
angle. The Jovian atmosphere, also, as will presently be 
seen, is probably much deeper, as it certainly is much 
denser, than that of the earth; and the heat radiated 
from the planet more than compensates, probably, for 
deficiency of solar heat. Hence it is fair to infer, finally, 
that the circulation of the atmosphere is much more active 
and powerful upon Jupiter than upon the earth. Profes- 
sor Hough reports drifting movements of white spots on 
his disc at the rate of 260 miles an hour, and these also 
in the direction of the planet's rotation. This state of 
things offers an explanation of the belted condition of 
Jupiter's equatorial region.* 

2. Jiqnter\s Betarded Development. — The data just 
presented concerning Jupiter's physical condition bring to 
view a stage of world-life very remote from that on the 
earth. The superior volume of Jupiter, if constituted like 
the earth, should give it a density 'many times greater than 
the earth, instead of one-fourth as great. Some remark- 
able planetary cause produces this great difference. The 
visible surface of the planet is constituted of moving and 

* On the remarkable bright "■ red spot" vit^ible on Jupiter's disc in 1879-80- 
1-2, see Nature, xxvi, 613, Oct. 19, 1882, for a notice of studies by Professor G. 
W. Hough, at Dearborn Observatory, Chicago, from his Annual Report. 



430 SPECIAL PLAXETOLOGY. 

changing vapors, which, by the rapid axial rotation, are 
drawn into parallel belts, especially in the equatorial 
region. These appear to exclude from view, perpetually, 
the real body of the planet. Moreover, the presumed 
relations of the atmosphere to the mass and surface grav- 
ity of the planet point out exceptional conditions. If 
the atmosphere on Jupiter sustains the same relation to 
the planetary mass as the terrestrial atmosphere to the 
earth's mass, it must be accumulated to nearly three times 
the terrestrial amount over each square mile of surface. 
Since Jupiter's mass is 309 times the earth's, while his 
surface is only 118 times as great, this atmosphere would 
therefore be accumulated over each unit of surface in 2.62 
times as great quantity as on the earth, and w^ould there- 
fore, for this reason, be 2.62 times as dense as the earth's 
atmosphere. But as Jupiter's gravity is 2^ times as great 
as the earth's, the actual density would be over 6 times 
as great as the earth's.* The Jovian atmosphere reduced 
to uniform surface density would reach an altitude .4123 
that of the earth's homogeneous atmosphere; that is, only 
2.075 miles. f All corresponding densities in Jupiter's 

*In the formula previously employed (p. 411)^ = 309: - = --—; — = 

2.254 {Annuaire, 1881). Hence p = P x 6.357; and if P = 30 inches, p = 190.71 
inches of mercury. This pressure is equivalent to that which would exist in 
the bottom of a shaft on the earth 91.8 miles deep, and would raise the tempera- 
ture of boiling water to 302° Fahr., which is somewhat less than the experimental 
result for saturated steam under the same pressure on our planet, 
tif M = the volume of the atmosphere of a'planet, 

s = the surface of the planet, 

m = mass of atmosphere. (If this is taken relative to mass of earth's 
atmosphere, then ni = mass of planet retative to earth's mass.) 

cr = density of atmosphere at surface of the planet. 

then h' = - approximately. 

„ m , ' m 

But 11=-: .-. h' = — • 

a S <r 

For Jupiter, the relative A'alues of these constants are ?n = 309: s = 117.9; a = 

6.3.57 (= p in last note) ; hence h' = .4123 h. 

To get h, the height of the earth's homogeneous atmosphere, we have fi = ^ 



JUPITER. 431 

atmosphere would be correspondingly lower than in the 
earth's. Tliat is, half the surface density would be reached 
at 1^ miles, while on the earth it is reached at 3| miles. 
The inference is, as Professor Proctor has shown, that the 
floating clouds of Jupiter's atmosphere must rest in com- 
parative proximity to his surface, instead of being elevated 
to atmospheric heights proportional to Jupiter's volunie. 
But astronomical observers inform us of phenomena which 
make it necessary to admit considerable depth to the cloud- 
layer. The special black lines in the spectrum indicate, in 
all the exterior planets, deep and dense atmospheres. 
Should we admit a depth of thirty miles, this would imply 
such a volume of atmosphere as would condense the sur- 
face layers to fifty times the density of platinum. We are 
compelled to assume, therefore, that a very peculiar plan- 
etary condition exists on the surface of Jupiter. Some 
cause is in action which at the same time greatly reduces 
the density of the planet and greatly increases the volume 
of the cloud-bearing envelope. 

Now, on the principles of the nebular theory, it is per- 
fectly legitimate to assume that Jupiter is lingering in the 
high thermal stages of planetary life. I have shown that 
progress on his surface must be 6|- times as slow as on the 
earth; so that if Jupiter had emerged as a separate body 
at the same epoch as the earth, he must lag far behind in 
development. It is quite supposable that though his 
planetary existence may have begun long before the 
earth's he may not, for all that, be so far developed, and 

But U =.b088;3T X I TT R3, and S = 4 tt R2; therefore h = .00127 R = 5.033 miles. 
This is given also by the height of the column of mercury in the barometer. 

To get .003837, relative volume of earth's atmosphere, we have 
Mass of atmosphere = im^^TTTy = .000000833 (Herschel), 

Density of air = ^. ^ ■ (Regnault). 

Olo.0( 

Density of air conipared with earth's density = .-r-p-.T; X -^m.- 

oii.bt 5.00 

Hence U = | tt R3 x 5.86 X 813.67 X .000000833 = | tt R3 x .003a37. 



432 SPECIAL PLANETOLOGY. 

may even have but recently reached the stage of incipient 
incrustation and cloud formation. The implied tempera- 
ture would retain his density at a comparatively low fig- 
ure, and would, besides, evolve a volume of cloud-support- 
ing gases which would greatly exaggerate the apparent 
diameter of the planet. I have shown that if possessed of 
the density of the earth, his diameter would be 53,000 
miles instead of 85,000, so that to present his present 
apparent volume, there must be an atmosphere capable of 
bearing clouds 16,000 miles above his solid surface. As 
no such atmospheric thickness is admissible, the planetary 
body must actually possess much less density than the 
earth; and this condition can be most naturally referred 
to heat as its cause. 

The luminosity of Jupiter seems to confirm this conclu- 
sion. Experiments made byZollner^on the light emis- 
sive powers of the moon and the planets exterior to the 
earth, after making all allowances for difference of dis- 
tances and diameters of the bodies, supply us with data 
from which the following table may be calculated: 

COMPARATIVE LIGHT-EMISSIVE PROPERTIES. 

Moon 1.000 Saturn 2.869 

Mars 1.539 Uranus 3.687 

Jupiter 3.598 Neptune 2.794 

Now, it is universally admitted that the lunar surface 
presents the condition of cooled and solid rocks, somewhat 
analogous to the surface of the earth. It is reasonable to 
assume that the moon's reflective powers are about as 
great as a surface of the lunar or terrestrial character can 
attain. Of what, then, must the surfaces of Jupiter and 
the remoter planets be composed to possess reflecting 
powers from 24- to 3^ times as great as the moon? It is 
safe to deny that any such reflecting powers are possessed 

ZoUner: Grundziige einer allgemeinen Photometrie des Himmels. Berlin, 
186L 



JUPITER. 433 

by planetary masses. The only alternative is the admis- 
sion that Jupiter and his giant companions possess still 
some amount of inherent luminosity, or are wrapped 
in envelopes possessing higher reflecting powers than 
solid planetary materials. 

The rapid rotation of Jupiter is evidence that tidal 
action, presently to be mentioned, has not gone far in 
destroying its rotary velocity. The younger and smaller 
planets have suffered much in this respect. Rapid rota- 
tion, according to our theory, is a characteristic of early 
periods of planetary history; and we here discover con- 
firmatory evidence of Jupiter's primitive stage of evolution. 

The most careful scientific examination of the physical 
condition of Jupiter's surface seems, therefore, to reveal 
the actual existence of a state of affairs supposed to have 
been long passed in the evolution of our own planet. The 
stormy stage of Jupiter is a fact before our eyes, while the 
stormy stage of the earth has been reproduced to thought 
only by a process of retrograde deduction. It would be 
vain to attempt to depict the precise nature of the events 
taking place on this gigantic mass, working out its plane- 
tary development in the solitudes of boundless space. If 
the planetary body shines with all the brilliancy of a 
molten globe, his light is screened by a dense veil of 
aqueous vapors. Were Jupiter's mass no greater than the 
earth's, we might not, perhaps, expect the condensation of 
aqueous vaj^or at so early a stage of cooling; but as I have 
shown, on a planet of such mass, the temperature of vapor 
formation would be as high as 302° Fahr. Whatever the 
condition of the planetary body, it is incandescent, and 
the gathered clouds are thick and dense enough to pre- 
cipitate their rains. Into what a furnace of consuming- 
heat are the rains falling ! Now, while we write, that 
stupendous and violent circulation of descending waters 
and ascending vapors which we have conceived as a ter- 
38 



434 SPECIAL PLAN-ETOLOGY. 

restrial scene long past, is in progress on an actual planet. 
The lightnings are darting and the detonations of the 
responsive thunders are resounding, and the noise is mag- 
nified by the six-fold density of the medium which trans-, 
mits it. To the naked eye, how mildly does Jupiter 
beam upon our earth ! What profound stillness reigns 
in the regions of the sk}^ where his majesty rides ! Can 
we gaze upon that silent, placid orb and imagine that the 
elements there are rending each other in very madness, 
and the roar of their clashing would stun the most insen- 
sible ears ? We have good grounds, however, to picture 
the home-life of Jupiter in the most startling colors. 

Not long since, cosmologically speaking, Jupiter was 
shining with cloudless self-luminosity. He was still a real 
sun revolving about our great common centre. There are 
regions in space from which our sun shines like a fixed 
star. From Sirius he appears as a star of a low order of 
magnitude. When the astronomers in those regions scan- 
ned our star some millions of years ago, they catalogued 
it as a double star. It had an attendant which revolved 
about the principal star in periods a little less than twelve 
of our years. So Alvan Clark, from our terrestrial stand- 
point, has detected a self-luminous planet revolving about 
Sirius. This is the Jupiter of the Sirian system. But its 
period is fifty years, or about four times that of our Jupi- 
ter. Thus we may contemplate Jupiter as marking dis- 
tinctly one of the necessary phases of a cooling cosmical 
globe. 

3. Tidal Action on Jupiter. — Jupiter's evolution must 
be perceptibly influenced by the tidal action of his satel- 
lites. The distances and masses of these satellites in re- 
lation to their primary are given in astronomical tables, 
and from these I have calculated their distances in rela- 
tion to our moon's distance from the earth, and their 
masses in relation to our moon, and also the vertical flue- 



JUPITER. 435 

tuations they are capable of producing on the water-covered 
planet.* The following table gives the results: 

Masses Densities Distances Tidal Effects 

Satellites. (Moon's = 1) (Moon's = .607) (Moon's = 1) (Inches) 

1 424 ,2009 1.084 88.21 

II 5835 .3890 1.725 33.07 

III 2.222 .3377 2.754 28 13 

IV 1.067 .2618 4.842 2.49 

The calculation was necessarily based on a planetary 
diameter as large as given in the tables. The result illus- 
trates the predominant importance of distance in tidal 
actions, since the second satellite, with more than a third 
more mass than the first, but with two-thirds greater dis- 
tance, has only three-eighths as great tidal efficiency. The 
first satellite, also, with only two-fifths the mass of our 
moon, and 20,000 miles more distant from the centre of its 
primary, exerts one and a half times the amount of tidal 
efficiency. This results from the fact that Jupiter's diam-' 
eter is more than eleven times that of the earth. 

It will be recalled that considerable importance has been 
attached to lunar action in the history of the earth, even 
since the attainment of an advanced stage of incrustation. 
A Jovian satellite possessing fifty per cent greater efficiency 
can not be overlooked as a working factor in Jovian evo- 
lution. The joint action of the first and second satellites 
is more than double our moon's influence; and the joint 
action of the three nearest satellites amounts to two and a 
half times our moon's influence on the earth, or a total 
fluctuation of 12t]- feet. Concurrences, or approximate 
concurrences, of tidal action very frequently happen. 

But the most important consideration in connection 
with the passing history of tlie planet, is the aeriform 



* Employing the same formula as previously, we have, for the first satellite. 
D-' (240000)3 (V2)- fji .000016877X309 r .^ ^^^ g 1 

7fi= (2600007 i =TUJ'' ■• m'^ m2S ' R = "'O^^ ^ 7r^2A25'' "'^'""'^^ ^ 

= 88.21 inches. Tlie calculation is similar for the other satellites. 



436 SPECIAL PLAXETOLOGY. 

state of the tide-moved ocean which conceals the body of 
Jupiter from our view. This yields with many times the 
facility of water, and the linear extent of the tidal deform- 
ation is correspondingly greater. If we could assume the 
aeriform envelope of Jupiter to be of the nature of pure 
air, which is 813.67 times as light as water, we should 
have, by dividing this number by 2.425, the relative inten- 
sity of gravity on Jupiter's surface, the actual density of 
the fluid subjected to tidal fluctuation. This density 
would be 335 times less than that of water, and would be 
moved, very approximately, to 335 times the extent. In 
other words, the first satellite must produce a fluctuation 
of 2462 feet; the second, one of 925 feet; the third, one 
of 784 feet, and the fourth, one of 70 feet. The concur- 
rent action of the first two must produce a difference 
of 6774 feet in the two diameters of the planet; and the 
concurrent action of the first three would cause a differ- 
ence of 8342 feet, or more than a mile and a half, in the 
flood-tide and ebb-tide diameters of the planet, and thus 
contribute something to the marked ellipticity which it 
reveals. 

Solar tidal action on Jupiter is so diminished as to 
produce a total fluctuation of only one and one-fifth 
inches if the planet were water-covered. Still, this is 
equivalent to a fluctuation of 334- feet in the aeriform 
envelope; and this amount of disturbance must be added 
to that caused by the satellites. 

The retardative influence of the Jovian tides seems to 
be now in the period of its highest efficiency. Jupiter, 
like any other planet in a state of rapid rotation, suffers 
the influence of a correspondingly large lagging angle in 
the tide ; and this augments the efficiency of the retarda- 
tive component of the tidal force. But, while Jupiter or 
any other planet exposes an aeriform envelope to be 
^.cted on, the free mobility of its parts presents, so far as 



JUPITER. 437 

its movements are concerned, a compensation for rota- 
tional velocit\^ When, however, any large part of the 
planet exists as a liquid or as a .viscous solid, a high 
rate of rotation must develop a large angle of lagging 
and a large retardative factor. A planet, therefore, like 
Jupiter, as we understand it, cloud-covered above and 
semi-liquid within, though still for the time being in- an 
early formative stage, exists at the same time, under 
those conditions of high rotation and semi-liquidity which 
tend to degrade most rapidly its rotational velocity. A 
relatively brief epoch, however, in the history of a planet 
having 309 times the mass of the earth, is numerically 
long in the history of the earth. Hence it is, as before 
suggested in reference to the dissipation of a planet's 
thermal energy, that a planet older than the earth in years 
is so much younger in development. 

So far, moreover, as rate of evolution depends on tidal 
retardation, a planet of large mass is more slowly influ- 
enced than one of smaller mass, by a given tidal efficiency. 
The horizontal component of the tidal force has indeed the 
advantage of acting at the extremity of a longer radius, 
but this advantage is only proportional to the first power 
of the radius. The resistance to it, for a given velocity, is 
proportional to the moment of inertia, or about the fifth 
power of the radius.* These relations tend very greatly 

* The moment of inertia of a sphere is measured by the mass into the radius 
of gyration, or, in common language, = Mk^. Among spheres of the same den- 
sity, and having uniform internal density, moment of inertia - kn r^ x tr"^ = 
1.6758 r^. That is, resistances to action of horizontal component of attraction 
on tidal protuberance are measured by 1.6758 times the fifth power of the ra- 
dius; but they are supposed applied at the extremity of the radius of gyration, 
which is equal to .6325?'. A unit of force applied here is equivalent to .5811 
applied at the extremity of the radius. Hence the moment of inertia of the 
sphere, supposed applied at the extremity of the radius, where the retardative 
force is applied (very approximately), becomes 1.6758r5 x .5811 = .973Crs. That 
is, the effective resistance of the moment of inertia is as the fifth power of 
the radius. 



438 SPECIAL PLAXETOLOGY. 

to a relative prolongation of evolution stages in the larger 
planets. 

4. Tidal Effects and Densities on Jupiter'' s Satellites. — 
I have heretofore pointed out the remarkable tidal influ- 
ence exerted by the earth on the moon, and it is proper to 
consider what part has been performed by the tidal influ- 
ence of Jupiter in the evolution of his satellites. Two 
circumstances point at once to the certainty that the tidal 
action exerted by Juj^iter must be enormous. His mass is 
309 times that of the earth, and 25,122 times that of our 
moon, and hence, other things being the same, the lunar 
tide on the earth must be multiplied by this number to 
show^ the magnitude of the Jovian tide on one of his satel- 
lites. Secondly, the satellites all possess a lower inten- 
sity of gravity than the earth, and for this reason, with a 
given diameter they present less resistance to the tide-rais- 
ing efforts of the planet. 

If we consider the case of the first satellite, and sup- 
pose, for the sake of comparison, that an ocean covers its 
surface, it wdll be evident Jirst, that so far as mass of the 
tide-mover enters into the calculation, it is 25,122 times 
that of the tide-mover in the case of lunar tides on the 
earth. Secondly, so far as concerns the effect of distance, 
it will be as the cube of 12 to the cube of 13, which 
is .7865. Thirdly, assuming, as heretofore, that the 
linear altitude of the tide is proportional to the radius 
of the tide-bearer, the value of this factor will be as the 
radius of the satellite to the radius of the earth — that is, 
as lire to 3963 which is .2967. Fownthly, the relative 
intensities of gravity on the satellite and on the earth will 
constitute another factor, and the height of the tide will 
be inversely proportional to the two intensities. These a 
little calculation shovrs to be as .05922 to unity, the recip- 
rocal of which is 16.89. The product of these four factors 
shows that the Jovian tide on the first satellite is 99,000 



JUPITER. 439 

times as great as the lunar tide on the earth. If we de- 
sire to express this in some comprehensible measure, we 
may assume, as heretofore, that the tidal linear fluctuation 
of the lunar tide is 58 inches; and from this it will result 
that the tidal effect of Jupiter on his first satellite is equiva- 
lent to an oceanic fluctuation of more than 90 miles.* 
This amazing result indicates a degree of prolateness in 
this satellite which possibly might be detected by the best 
measurements; though 90 miles, at the distance of Jupi- 
ter, subtends an angle of only one twenty-fifth of a second. 
That is to say, if the satellite, while making a transit 
across the planet's disc, has an angular diameter of 1".02, 
it should have at its elongations a horizontal diameter of 
r'.06. 

To the tidal effect must be added the tidal effects of 
any other satellites when in conjunction with the first one. 
A little calculation shows that the tidal effect of the 
second on the first, when in conjunction, is over fifty-three 
feet of water, t 

With this disclosure of the tidal distortion of the 
Jovian satellites, we can appreciate the certainty of their 
rapid approach to a state of synchronistic rotation. If 
this state was not attained before the disappearance of 
the water belonging to one of them, the tidal oscillations 
must have acted with most destructive energy upon the 

* We may adapt the formula heretofore used, and abbreviate the operation 
as follows : In the expression 

/ = T .— •-. — • -^. 
' rf3 ' R3 ' w ' m' 

d — distance of first satellite from Jupiter, 

r — radius of the same, and m = its mass, 

/ix = the mass of Jupiter. 

Hence, ^ - 58 X g; X [-!» X ^^ X ^^^^ = 5,743,000 inches = 90.64 

miles. 

t Applying still the general formula, 



440 SPECIAL PLAKETOLOGY. 

solid crust. The tidal movements of the crust itself 
developed constant fissures through which the molten inte- 
rior escaped in enormous ejections, and the planetary 
waters poured within, developing explosive energy suffi- 
cient to hurl fragments beyond the sphere of the satellite's 
attraction. If the volcanic action continued after the 
retirement of the water, as I have assumed in the case of 
our moon, a process of crater formation must have taken 
place similar to that occurring on the moon, but as much 
more violent as the tidal efficiency was greater on the 
Jovian satellite. It is to be presumed, therefore, that it 
presents a disc more fearfully scarred than that of our 
moon. The enormous irregularities of the surface present, 
in the course of a rotation, various aspects toward the 
sun. In some situations the exposures are such as to 
reflect much more light than in others; and hence the 
brilliancy of the satellite varies, as has been observed. 
But, in this view, the same aspects should reappear with 
each return of the same exposure. If these reappearances 
should be found correlated only with the orbital move- 
ments, the fact would indicate that the axial rotation 
moves synchronously with the orbital revolution. If it 
should appear that the recurrences do not correspond 
with orbital positions, it must be inferred that synchro- 
nism does not exist; and then the period of the recurren- 
ces might afford a clew to the satellite's period of rota- 
tion. But on theory it may be conjectured that tlie 
recurrences stand only in relation to orbital movements.* 
A study of the densities of these satellites affords some 
very suggestive results. The densities have been already 
included in a table of the satellites on page 435. Taking 
the earth's density as unity, they range from one-fifth to 
two-fifths. The density of our moon is three-fifths. Sat- 

* Father Secchi, nevertheless, states that he has observed a rotation of some 
of Jupiter's satellites (Le Soleil, ii, 405). 



JUPITER. 441 

ellite IV, which has about the mass of the moon, has less 
than half its density. Satellite III, with two and a quar- 
ter times the mass of the moon, has little more than half 
its density. Now, as these satellites cannot, with any 
probability, be regarded as enshrouded in warm vapors, 
or even in a high thermal state, they are in a fair condi- 
tion to compare with our moon; and when we find them 
possessing a greatl}^ lower density than our moon, we are 
constrained to believe them composed of lighter materials. 

Again, Jupiter and his satellites might be conceived as 
formed of materials of nearly the same density. But as 
Jupiter possesses 59,250 times the mass of the first satel- 
lite, and 11,310 times the mass of the largest satellite, the 
vast condensation existing in his interior should give him 
a much greater density than any of his satellites. But, 
on the contrary, his density is only one-fourth that of 
the earth. This remarkable fact affords further indication 
of Jupiter's high thermal state. 

If, as we argue, the materials of Jupiter's satellites 
embrace a larger proportion than the earth of aqueous 
and gaseous compounds, then the solid and cooled body of 
one of these satellites would be less capable of effecting 
a complete absorption of the fluids, as has taken place on 
our moon. It is, indeed, quite supposable that the fluids 
should exist in such proportion as to suffice for saturating 
the pores of the cooled planet, and supplying a surplus to 
cover its surface. We must bear in mind, then, the 
possibility that these and other and remoter satellites 
of our system remain actually water-covered. A vapor- 
laden atmosphere might possibly restrain within it suffi- 
cient solar heat to keep such a watery film, or partial film, 
in a state of liquidity; but, on the contrary, it is almost 
certain that the thin atmosphere of these light bodies 
admits of radiation so free that any surface water is held 
permanently in a solid state. The possibility of fields of 



442 SPECIAL PLAITETOLOGY. 

ice ocean-wide renders it jDossible that the sun's light 
should be flashed to us in certain situations of the satel- 
lite, giving it a temporary excess of brilliancy. Wide 
areas, with only the reflecting power of crushed ice or 
Alpine neve, might, by contrast with the darker upland 
areas, as is aptly illustrated by the snow-covered polar 
regions of Mars, produce that variation in reflecting 
power which, otherwise, I have attributed to mere topo- 
graphical configuration. 

§6. THE ULTRA-JOVIAN PLANETS. 

Much that has been said of Jupiter may be applied 
with even increased propriety to all the planets exterior to 
him. The ringed planet with a diameter more than nine- 
elevenths the diameter of Jupiter, has less than one-third 
of his mass, and possesses, consequently, only half its 
density, or .129 that of the earth. This is only three- 
fourths the density of water, while Jupiter possesses one 
and three-eighths the density of water. Gravity at 
Saturn's surface is, therefore, 1.14 that on the earth. 
Moreover, the surface of Saturn is veiled in clouds like 
that of Jupiter, and analogous belts, though fainter, are 
generally seen drawn across his disc. His relative lumin- 
osity is but a little less than Jupiter's. The condition of 
Saturn is, therefore, more extraordinary than that of Jupi- 
ter. If we found reason for supposing the latter to sub- 
sist still in a primitive and highly heated stage, the con- 
clusion seems, at first thought, even better suited to the 
case of Saturn. It must be admitted that in the case of 
both these planets thermal intensity would suffice to pro- 
duce the low density observed, only on the supposition 
that it approaches somewhat that of the sun, whose den- 
sity is the same as Jupiter's, and twice that of Saturn. 
But a heat approaching that of the sun is entirely inadmis- 



THE ULTRA-JOVIAN PLAI^ETS. 443 

sible, since this would dissipate the aqueous vapors which 
envelop these planets, and would impart to their light 
spectroscopic properties truly solar. There is no probable 
way of accounting for the low density of Saturn but to 
admit that it is 3omposed, in larger proportion than the 
earth, of substances possessing a low specific gravity. 
This conviction carries our thoughts back to the primitive 
nebular condition of our system, and recalls a conclusion 
of which we have heretofore been frequently reminded, 
that the denser matters would gravitate toward the centre 
of the nebula, leaving the lighter to enter into the forma- 
tion of the earlier planetary rings. Then it is supposable, 
also, that Saturn still lingers in a high tliermal stage, and 
that his cloudy envelope, like that of Jupiter, depends on 
the action of internal heat, and argues the stage of the 
cosmic rainstorm on the planet's surface. All the evi- 
dences of primitive thermal conditions which have been 
pointed out in Jupiter and his satellites are repeated in the 
system of Saturn, except that Satuni's double age intro- 
duces a changed relation. 

Of the planets Uranus and Neptune, our information 
is comparatively imjDerfect. They are, however, well known 
to be of nearly equal volume and density, having diameters 
less than half that of Saturn, and densities approximating 
that of Jupiter. They are thus but little denser than water.* 
The inherent luminosity of Uranus is even greater than 
Jupiter's, and that of Neptune is equal to Saturn's. It is 
the opinion of Proctor that the reasons for assigning a 
high thermal condition to Jupiter constrain us to reach a 
similar conclusion in reference to these jDlanets. 

This conclusion, however, is not the only one to be sug- 
gested. The theory of partial incandescence in Jupiter is 

*The Annualre du Bureau des Longitudes for 1881, however, gives the den- 
sity of Neptune as .410 compared with the earth, while that of Uranus is .234, 
and that of Jupiter .242. 



444 SPECIAL PLAXETOLOGY. 

admissible. But Saturn is both an older planet and a 
smaller one. It should be further advanced in its evolu- 
tion. But its density is even less than that of Jupiter. 
We cannot pursue the line of reasoning employed in 
Jupiter's case, and infer still higher incandescence than 
we may admit in Jupiter. The embarrassment is repeated 
and augmented as we recede from Saturn to Uranus, and 
from Uranus to Neptune. We seem constrained to seek 
some other explanation more in harmony with the doctrine 
of successiveness in planetary origins and the necessity of 
some relation between age, amount of internal heat, and 
rate of cooling. 

The great facts in the case of the three outer planets 
are enormous bulk, low density, exceptional brilliancy and, 
as is probable, great relative age. Any hypothesis con- 
cerning their physical condition must harmonize these four 
facts. Now, our theory requires a gradation in densities 
corresponding with approximation toward the centre of 
the system. The superior age of the remoter planets 
requires them to be more advanced in their evolution, and 
their superior mass requires them to be less advanced. 
Their actual condition is the resultant of these two require- 
ments, and it may not be possible to ascertain whether it 
is a stage of world-life more or less advanced than that of 
the earth. 

Apparently, however, strong reasons exist for regarding 
the ultra-Jovian planets as far more advanced than the 
earth. iVn attempt to calculate the relative duration of 
their cosmic periods brings out unexpected results. Any 
precise calculation is impossible, in consequence of their 
relatively low density and the impossibility of ascertaining 
their true volumes, arising from the vapors which con- 
ceal the true planetary bodies. But, assuming the dimen- 
sions of these planets to be such as are usually given in 
the tables, and making the calculations according to the 



THE ULTRA-JOVIAN PLANETS. 445 

principles heretofore explained, we find that the cosmic 
periods of Saturn exceed those of the earth by only one- 
seventh, while Uranus and Neptune have cosmic periods 
of only three-quarters the length of the terrestrial periods. 
Those planets held primitively many times the quantity of 
heat possessed by the primitive earth, but their relative 
surfaces gave them power of radiation in equal or greater 
ratio. It has been generally conceived that cosmic periods 
were longer on all the remoter planets, but, after allowing 
for all chances of error in calculation, it appears certain 
that the ultra-Jovian planets advanced at about as rapid a 
rate as the earth. Their vastly superior age seems, then, 
to afford very strong evidence that they have not only 
passed the Jovian stage, but even the terrestrial. The 
vapors, therefore, which envelop them cannot arise from 
any heat comparable with that supposed to be perpetuated 
in the planet Jupiter. 

Now, will it be allowable to entertain these concep- 
tions of Saturn, Uranus and Neptune, and hold at the same 
time to the partial incandescence of Jupiter? Can we 
maintain heat as the cause of Jupiter's low density, and a 
cooled aqueous condition as the cause of the low density 
of the remoter planets? This, I admit, is a question 
which ought to be considered open. Perhaps Jupiter, 
also, is a cooled aqueous globe, instead of a globe in its 
high thermal and stormy stage. Assuredly, we must con- 
cede to Jupiter a much larger proportion of water and 
gases than the earth possesses; but must we affiliate the 
planet in constitution and stage of development with 
Saturn more than with the earth and a certain stage in its 
life history? In passing from Jupiter to Saturn the dis- 
tance is more than doubled which separates Jupiter from 
us. If the interval which separates Jupiter from us justi- 
fies all the assumed contrast in conditions which has been 
indicated, the greater distance between Jupiter and Saturn 



446 SPECIAL PLANETOLOGY. 

justifies an equal contrast, and all the more when we con- 
sider that Jupiter's cosmic periods are twice the length of 
Saturn's. But the comparison is not alone between Jupi- 
ter and Saturn, but between Jupiter and the group of 
remoter planets. What does the mean distance of this 
group from Jupiter suggest and demand in reference to 
comparative conditions? AYhat does the extreme dis- 
tance demand? Uranus is four times as remote from the 
earth as .Jupiter is, and Neptune is more than seven times 
as remote. There is space for enormous contrasts of con- 
ditions, even with cosmic periods as long as Jupiter's. 

If Saturn is composed of materials less dense than 
those which make up the bulk of our earth, what are 
those materials likely to be except water, atmospheric air, 
perhaps with the constituents mixed in different propor- 
tions, gaseous hydrocarbons and carbonic anhydride? 
In addition, there must be smaller proportions of the 
various solid constituents of the earth. If Saturn were 
composed wholly of water, his density would be greater 
than it is in consequence of central condensation. If he 
possessed, in addition, a superior allotment of gaseous 
constituents, they would clothe the water^^ globe with an 
atmosphere. In the centre of the globe of water would 
be accumulated all the solid constituents. Incrustation 
would be the freezing of an icy film upon the watery sur- 
face; but it would begin late and onh^ at a much lower 
temperature than rocky incrustation. The prolonged 
liquidity of the planet would prolong the process of con- 
vective cooling, and thus accelerate plai>etary refrigera- 
tion beyond the rate already indicated. So old a planet 
cooling by convection should have passed the thermal 
stage. Enormous internal condensation might deprive 
some of the watery mass of the properties of a liquid, 
and thus arrest partially the convective process, while 
cooling would proceed by radiation from the surface. 



THE ULTRA-JOVIAN PLANETS. 447 

The incidents in the formation of an icy crust would pre- 
sent a complete analogy with the history of terrestrial 
incrustation. A watery planet would never absorb com- 
pletely its atmosphere, especially if we assume a greater 
relative volume on such a planet. At all stages of cool- 
ing, therefore, a voluminous atmosphere would be present, 
and at all temperatures the vapor of water would rise and 
load the atmosphere with clouds. The cloudy envelope 
would increase the apparent diameter of the planet, and 
lead to an underestimate of its density. Even with the 
central condensation due to the mass of Saturn, the actual 
mean density might not be greater than what we actually 
observe. At the same time the reflecting power of the 
cloudy envelope might impart to the planet that extra- 
ordinary degree of luminosity which Zollner has deter- 
mined. The relative brilliancy of Saturn ought, in this 
view, to be much greater than that of the rocky disc of the 
moon. If these considerations are applicable to Saturn, 
they are quite as applicable to Uranus and Neptune. 
Uranus is said to present some spectroscopic indications 
of a peculiar character. In reference to this, we can 
understand that, according to our theory, the two outer 
planets should contain progressively more of the gaseous 
constituents, but this is all which can at present be 
suggested. 

Should the views here set forth be true respecting the 
excess of watery and aeriform constituents in these plan- 
ets, then tidal action upon their surfaces could never have 
produced, since their fire-mist stage, the retardative effects 
experienced by planets which pass long periods in a state 
of molten viscosity. As long, also, as their w^aters main- 
tained an unfrozen state, the retardative action of their 
tides would be small compared with terrestrial oceanic 
tides, since no continental barriers to tidal motion would 
be interposed, and the onl^ retardation would arise from 



448 SPECIAL PLAXETOLOGY. 

the low viscosity of water. When incrustation (ice forma- 
tion) began, even this action of watery tides would be 
greatly diminished, and would finally cease. Much, there- 
fore, of the primitive rotational velocit}^ of such planets 
must be retained to the present epoch. This inference 
agrees with our best observations. 

In view of these considerations, it does not seem a 
violent supposition to assume an aqueous and cold condi- 
tion for Neptune, and a semi-aqueous and heated condi- 
tion for Jupiter. Then, further, the similarity of the 
indications from Saturn, Uranus and Neptune is signifi- 
cant. If they were still in planetary progress they would 
not exhibit the same stage of evolution. How could 
identity of condition exist unless that condition be a 
planetary finality? No planet can pass a state of total 
refrigeration. Perhaps Neptune attained this and re- 
mained changeless. Uranus later attained it and remained 
changeless. Saturn, even, has attained it, and the three 
oldest planets accordingly have run their courses equally, 
and have alike attained the death which levels all dis- 
tinctions. 

Under any theory the four remoter planets present 
existing conditions widely different from those of our 
planet. In the view here suggested, the three remoter 
planets evince conditions of constitution so diverse from 
those of the earth that the terrestrial state can never have 
been assumed, though the terrestrial stage may long since 
have been passed. These planets roll on through the still 
and changeless winter of their planetary life — globes of 
crystal wrapped in stagnant fogs which the sun's feeble 
ray is unable to stir to the movements which characterize 
a living world. 



THE ULTRA-JOVIAJs^ PLACETS. 



449 









Radius, miles, 
and Earth=l. 



Surface. 
Earth = 1. 



M. 
























1 


§ 


c2 


25 


§ 






.- 


. 


o 


Volume. 
Earth =1. 


$ 


fe 












o 










N) 


Vt 


?o 


M^ 


-^ 


o 


CPl 






w 


CO 






















M 


■b 


P 


i° 


P 




o 


o 


b 


bo 


b 


Mass. Earth=l 


O 


o 


-a 


VI 


?o 


O 


GO 




o 


crt 


or 




O 






















Density. 


^ 


C: 


-7 


^3 


ks 




ir 


1-' 


J-' 




Earth = 1. 


fe^ 
























05 


»4 


CO 




ts 




-I 










*-ti 




•O 3. 












•^ p* i"^ S 




Solar Intensity. 






o n 


CC CD 


O (D 


ro c 


O CK 




§"£- i'^. 


?^£- 


Earth=l at 


»^ 






■■.]■; 












mean. 






S8 


w-j! Sos 


Sg 


cob 




§§ bg 


^p 

or or 








h-k h-i 




O 4^ 










*?! 






















Cosmic Periods. 


o 


iii 


1 


:2 


;^ 


J*°l^ 


^ 




o 


3 


W 


Earth=l 


i 


S 


iS 


or 


g 2 


^ 


^ 


o 


icj 


§5 












w 






Iri 






Solar Tidal 


"^ 










ill 




J^S !"' 


^^ 




Efficiency. 


> 












CO'" 


1^1 


CO 


is 


Earth=^l. 










OCH-.^ 


<0 


?r 


s?g 






Linear fluctua- 










is^»? 


CO 


ho 




.t^ 2 


tion of Solar- 












^w^. 


l-i 


^p 


s-«:^ 


-a 


;^ % 


tide. 












?F- 


ti 


^ 




^. 


s 


Earth^l. 
























Atmospheric 




j-i 






1-^ 


p 




Q 


I-' 


b 


■ 


Pressure. 




§ 


S 


or 


^ 


?s 


CO 


»§ 


g 


00 


Earth=l. 




-5 


CO 


VI 


-3 




00 


o 


o 


Ot 


♦S) 




















1 




p' 


Height of 




g 

M 


^ 


ui 


to 




.*^ 


bo 


i 


p ^ 


Barometer. 
Earth =30. 






^ 


or 






0^ 


Oi 


o 


o. • 






s 

kS 


2 


3 


g 


i 


^ 


ss 


K) 

H 


*a 


O D* 


Water hoils. 
Earth=212° 














s 


" 




§ 


i 




Fahr. 




CO 


io 


b» 


4». 


c;' 


c;» 


bo 










! 












- s 


Height of 




•r* 


Oi 


-C! ! ^ 


^s 


>-' 


J2 


p 


or 


Homogeneous 






i 


^ 1 i& 


i 


^ 


S 


i 


s 


s.s 


Atmosphere. 





450 SPECIAL PLAJ?"ETOLOGY. 

Remarks on the Table of Planet ogenic Constants. 

1. The "cosmic periods" are identical with relative 
intensities of gravity on the surfaces of the planets; since 
^'=: 9'^'— 2^ where g' , m and r are gravity, mass and 
radius of the planet, and g, M and R are gravity, mass and 
radius of the earth. But this expression is equivalent to 
^ ' M * 1> where s and S are surfaces. But, making the 
terrestrial values g^ M and S equal to unity, we have for 
relative gravity, g' = j, which is identical with the expres- 
sion for relative cosmical periods. 

2. The "linear tidal fluctuations" are intended to show 
what would take place on ocean-covered bodies similar to 
the earth, and not to imply that such tides have ever 
actually existed, in each case, or ever will exist. Still, 
about this we can neither affirm nor deny positively. They 
stand, at least, as measures of tidal forces and tidal effects 
in some form. 

3. The values entered in the last four columns cannot 
be very exact. They rest on the assumption of physical 
conditions analogous with those of the earth; but this we 
know is not generally the fact. Besides the differences in 
the ratios, in different parts of the system, between the 
fluid and solid constituents, the differences in thermal 
conditions and states of matter vitiate the results ob- 
tained, especially in regard to the remoter planets and the 
sun. The same is true respecting the column of cosmic 
periods. Still all these results are suggestive and interest- 
ing. 



CHAPTEE IV. 

PLANETARY DECAY, 

OR COSMIC CONDITIONS MORE ADVANCED THAN THE 
TERRESTRIAL STAGE. 



Physico-inechanical laws are, as it were, the telescopes of our spiritual eyes 
which can penetrate into the deepest night of time, past and to come.— Helm- 

HOLTZ. 

Everything cosmical must be gradually decaying.— P. G. Tait. 

§1. EXTREMELY ERODED CONDITIONS. 

THE erosion of the terrestrial surface has been in 
progress ever since the emergence of the oldest land. 
The chief erosive agents are waters, frosts and winds. 
The action of these agents is everywhere facilitated by 
changes in the state of cohesive and chemical aggregation 
of the parts. The forces of cohesion and chemism are 
influenced by temperature, and this sometimes varies with 
the rate of escape of heat from the planet's interior. The 
total amount of erosion which the earth's surface has 
endured is measured by the total amount of sedimentation 
which has taken place since land first appeared. The whole 
mass of the existing sedimentary rocks measures only a 
part of this denudation, since older sedimentary rocks 
have been repeatedly reduced to sediments and reelevated 
in later ages. Not only have vast volumes of earlier sedi- 
mentary formations been worn out and rewrought into 
later formations, but the entire mass of the primitive fire- 
formed crust has disappeared — on its lower surface by 
refusion, but on its upper surface by erosion and chemical 
dissolution. 

451 



452 PLANETAKY DECAY. 

During the progress of these erosions, mountain masses 
have shrunken in dimensions, continental surfaces have 
been lowered, and oceanic basins have been progressively 
filled — more especially along the continental borders. 
There are good geological grounds for believing that ex- 
tensive land areas have disappeared * — partly by erosion, 
but sometimes by subsidence — while the progressive 
emergence of the principal continental masses has been 
going forward. All geological evidence, however, points 
toward the conclusion that no general interchange of 
oceanic and continental regions has ever taken place. 

The first effects of terrestrial erosions lie exposed to 
our observation on a vast scale. Some of these are results 
whose earlier history reaches back into the middle or begin- 
ning of Mesozoic Time. The old Niagara gorge began, 
probably as soon as the drainage course was established 
from the Superior Sea to the Gulf of St. Lawrence. This 
could have been even in Palaeozoic Time. The Ohio, 
Upper Mississippi, Hudson, Connecticut and many other 
river valleys began to be excavated at epochs equally 
remote. The work in all such cases has been in progress 
to the present time, except so far as interrupted by the 
conditions of the Glacial Period. In our trans-Mississippi 
states and territories are records of erosion equally 
ancient. But the most conspicuous cases probably date 
from the Mesozoic or Cienozoic Time. The stupendous 
canons of the Colorado, Green, Columbia and other west- 
ern rivers are features Mesozoic or C^enozoic in their ori- 
gin, but progressively worked out by agencies which, to 
our day, have never ceased their activity, however their 
forces are diminished; as the monuments of the genius and 
power of classic Greece connect themselves by historic 
continuity with the feebler activities of modern Greeks 
exerted under the observation of the world. The broad, 

* See the author's Sparks from a GeologisVs Hammer^ 122-51. 



EXTREMELY ERODED CONDITIONS. 453 

scarred and desolated plateaus of the West testify to the 
removal of thousands of cubic miles of the ancient sur- 
face. Some of the greatest of these denudations have 
taken place in later Tertiary time. The records of erosions 
begun in a later geological period are universally exposed 
to view. All except the fundamental features of our 
topography have been carved out by erosive agencies in 
post-glacial times. 

The mode of action of these agents is matter of daily 
observation. Every turbid summer torrent reveals the 
transportation of portions of the disintegrated surface of 
the earth from higher to lower levels. Some of these 
sediments find their way into the bottoms of lakelets and 
build up the foundations of marshes and alluvial lands. 
Some are borne to the larger streams to be deposited on 
their flooded flats, or carried to the Missouri, the Ohio and 
the Mississippi. The Mississippi, like the Amazons, the 
Ganges and the Nile, contributes its annual layer to a 
thickening delta, and bears the remainder of its sediment- 
ary burden to the sea. In the Gulf of Mexico it builds a 
bar by the annual accumulation of sediment, which in its 
growth has encroached sea-ward 338 feet a year. It has 
already grown far from the ancient Gulfshore, and carried 
its foundations into the deep waters of the Gulf. Dr. J. 
E. Hilgard has shown that the deep basin of the Gulf 
approaches very near to the present bar and present ter- 
mination of the jetties of Eads.* 

By such erosions and transportations the continents are 
continually lowered and the sea basins are repleted with 
materials taken from the land. If elevatory forces were 
as efficient as formerly, the relative levels of the land and 

*J. E. Hilgard: Tlie Basin of the Gulf of Mexico, ''Science" ii, 138-40, 
March 26, 1881, with a chart. The depth of the water into which the bar has 
reached will cause hereafter a slower development than in earlier times. The 
efficiency of the jetties will therefore remain without serious diminution, for a 
period comparatively prolonged. 



454 PLAXETAEY DECAY. 

sea bottom might be retained; and the relative altitude of 
the land might be increased. But the elevatory forces 
must undergo diminution, and the continents must conse- 
quently be slowh^ transferred to the ocean basins. If the 
amount of surface water remains undiminished, the sea 
level must slowly rise, and the time must come when the 
fuller ocean will overflow the shrunken dimensions of the 
land. When the work of erosive agencies is accomplished, 
the sea will be universal, as it was before the nuclear 
wrinkles of the continents first emerged. The earlier and 
the later conditions of our planet, therefore, present it 
wrapped in a sheet of water. The continental lifetime is 
only a temporary emergence of sea bottom accompanying 
slight movements occasioned by stresses of the earth's 
interior. Organization seizes the opportunity to rest its 
foot on the unsteady land; it plays its evanescent role, 
and the continental swell settles back into the ancient bed 
from which it lifted its head only for a temporary relief. 
The ancient ocean still lives; the tidal wave still rolls; the 
sun rises and sets as before; the moon waxes and wanes: 
the storms in the atmosphere have died; the sounds ol 
animated nature have perished; life conceals its perpetu- 
ated activites in the voiceless depths of the all-subduing sea. 
In the annexed diagram A B represents the mean level 
of the land, E F, the present sea level and C D, the sea 
bottom. When the continents have been levelled to the 
present water's surface E P, the ocean will stand at I K, 
282 feet deep over all the land. The land above the pres- 
ent ocean level, if thrown into the sea, would raise its bot- 
tom to G H, 384 feet. These results rest on Keith Johnson's 
estimate of about one-fifth of a mile for the mean height 
of the land. If we take Kriimmel's more recent esti- 
mates,* we shall have the mean elevation of Europe 300 

* Kriimmel, Gottinger Acad. ; G. Leipoldt, Peternianns Mitthnlungen, 
Apr., 1875, Nature, 15 Apr., 1875, and 3 Feb., 1879, 348-9; Amer. Jour. ScL, III, 
ix, 482. 



EXTREMELY ERODED CON-DITIONS. 



455 



m., Asia and Africa, 500m., America, 330m., Australia 
250m., giving a mean of 426m., or .2646 mile. This 
would cause the ocean to stand at IK 373 feet above its 
A B 





f 








-373--— 


^..... 


JK 


...|-_.. 


—--^— 




-p 








F 


5 


o' 


CO- 








of 
1 







-.Jkl-._ 


r-- 




M^ 




V 


N 
















i 

CO 














._-i- 


. ._\V..- 


G 


o08-- 




M 



Fig. 59. The Disappearance of the Land. 
present level, if all the land were thrown into the sea, and 
the sea bottom would be raised to GH, 509 feet. 

The plane M N which has an amount of land above it 
equal to the capacity of the ocean's basin below it — that 
is, the plane which would represent the surface of the 
land if it were completely levelled down, passes, if we take 
Keith Johnson's estimate of the mean altitude of the land, 
1.42 miles — the distance P M' — below the present level 
of the sea; or if we take Kriimmel's estimate, 1.41 miles. 
Hence a complete levelling of the land surface would cause 
the sea to stand 9541 feet above the land, according to 
Keith Johnson's data, or 9450 feet, according to Kriim- 
mel's estimate of the present mean height of the land. 
The deposit of this amount of land on the ocean's bottom 
would raise it to M N, 3860 feet, or 3950 feet, according 
to the data used.* 



* Let ! = relative surface of land = .167, 
w — relative surface of water = .733, 

h = mean height of land = E A = 



.2 mile CJohnson), 
.2646 mile (Krummel), 



456 PLAls^ETARY DECAY. 

Such are the tendencies of erosive agencies on the ter- 
restrial surface, and such tendencies must exist wherever 

d = mean depth of ocean = P C = 2.538 milep, 

z = depth of uniform land surface below present sea level = E M, 

y = depth of sea over uniform land surface = M I, as appears, 

c = C G = depth of covering on sea bottom when land is lowered to E P, 

€' = M'C = depth of covering on sea bottom when land is lowered to MN, 

a; = E I = rise of sea level when land is lowered to E P, 

a/ = rise of sea level when'laud is lowered to meet sea level. 

I. Suppose land levelled to E P, the present sea level. 

Then x (w -\- I) = Ih., or, since iv ■=\-l = \, 

- = "' = -^e^ X .; %,, \ = ] ;«^54 mile ^^im feet i ,,„, p,,,,„, ,,, ,„,,, 

26T -* -^ ' 

And CIV - Ih ore- — - ' -^^^ ^ - J .07285 mile i _ j 3S4.6 feet ( -^pnth 

A.nacu -ifi.oic^ ^ - ^^^ - J ^gggg ^.j^ ^ _ ^ g^gg ^^^^ J _ depth 

of'deposit on ocean's floor. 

II. Suppose land levelled to meet rising sea level. 

Then I (h —x') = ivx'. whence x' = — -y = lh = xas above. 

III. Suppose the land levelled to uniform land surface M N. 

Now, the land surface will be even all over the globe ; the present volume 
of the ocean will be of uniform depth, and we shall have 
y (w -{-I) = wd, or, since w -\- I = 1, 
y = wd = .733 X 2.538 miles - 1.8604 mile = depth of sea all over the earth. 
Also to find E M, depth of uniform land surface below the present sea level, 
I (h -f z) = IV (d — z) and Iz — ivz - wd — Ih. 

••■«=^^^=-''-'*=-'88x2,5S8-..6Txj;|,4=JJ:S} mile 

= depth below present sea level of uniform land surface, 

or 1 8(504 — i ^•^^''^ i - i -^^-^^ ^"^^ (. - i ^^^ ^^^* I re«ultina «ea level above 
or, l.Bb04 -J J gg^.^ ^ - -| Q~Q^ j^^.jg j- _ -j 3^3 jpg^ J- resulting sea levei aDo\ e 

present sea level — x = x'. 

That is, the depth of the overflow is the same as when the land is levelled 
only to the present sea level. This must ob\iously be so, since after the level- 
ling of the land meets the rising sea level, all further lowering of the land is 
simply a change of place of matter within the mass of ocoan waters. Hence the 
line of meeting of the lowering land surface and the rising sea level ought to 

be as shown above, ^ o^o r feet above present sea level. This is the highest 
which the sea level can be made to attain. 

Also, to findM'C, the depth of the deposit over the ocean's floor, 

c'lv = I (h-^z) w^hence C = -^— -^ — '- - 



2„. J .2 + 1.8066 ) 

• 1.2646 + 1.7893 ^ ^ , . j3n „,ne ; ^ j 3860 feet , ^ ^j^ ^^.^^ ^^^^^-^ fl^„, ^ 

.733 ( .7481 mile \ i 39o0 feet ( ^ 

M'C. 
But this is also given directly, since M'C = PC — PM' = 2.538—-. i^-^gg-j j- = 



.731 
.7483 



as before. 



EXTREMELY ERODED CONDITION'S. 457 

ocean waters are accumulated. On Mercury^ and perhaps 
also on Venus, the intensity of the solar rays may prevent 
water from existing except in the form of clouds. Denu- 
dation, therefore, could not have Ifegun. It is still quite 
conceivable, however, as before stated, that the freedom 
of radiation in the upper atmospheres of both these plan- 
ets, and especially of Venus, may be such as to condense 
permanent envelopes of aqueous vapor and thus screen 
the surfaces of the planets from the severest intensity of 
solar radiation. In such case, there must be also some 
amount of precipitation and a corresponding amount of 
erosion. 

Some reasoning as to the conditions which may have 
affected precipitation on the moon have been presented in 
the section devoted to the geology of the moon. It seems 
supposable that during a portion of the moon's non- 
synchronistic period vapors condensed, rains fell and seas 
of some extent existed. The great tidal influence expe- 
rienced by that body, however, rendered it impossible that 
land masses should not be raised to great altitudes above 
the sea level. The enormous height of the tides in any 
extensive ocean must, therefore, have eroded the shores 
and the bottoms of shallows with intense energy. If the 
earth was still a sun to the moon, its heat must have 
caused an extraordinary amount of evaporation and con- 
sequent precipitation, and the agency would have eroded 
the uplands to a corresponding extent. Or, if water 
remained on the moon after the synchronistic period had 
been reached, — something which I have not assumed, — it 
fled to the farther side, but underwent most copious 
evaporation through solar influence during each alternate 
fortnight. Great evaporation implies great precipation; 
and it is hardly supposable that some of these rains did 
not fall on the land side, and thus serve as an efficient 
agent of erosion. But there is reason to doubt whether 



458 PLAl^ETARY DECAY. 

the moon's surface in non-synchronistic times ever expe 
rienced sufficient composure to allow a proper ocean to 
rest upon it. Not improbably, the water, through the 
constant ruptures of the crust, and outbursts of molten 
matter, was kept in a constant process of evaporation and 
condensation, until the solidified portions became suffi- 
ciently voluminous to receive the water into their pores. 
In this case, the records of all aqueous erosions which 
ever took place on the moon have become obliterated or 
disguised by the violence and duration of eruptive action. 
Mars is the only one of the planets besides the earth 
on whose surface aqueous erosions are somewhat certain 
to have taken place. The largest of the satellites of 
Jupiter, with a diameter of about 3700 miles, and the sixth 
of Saturn, with a diameter of 3800 miles, are both con- 
siderably larger than Mercury, and may easily be conceived 
to have passed a thermal condition suited to aqueous pre- 
cipitation and erosion. But the enormous tidal power 
exerted on these satellites by their primaries renders still 
more probable than in the case of our moon, the hypothe- 
sis of incessant physical violence during their non-synchro- 
nistic period, and the absence of all proper aqueous ero- 
sion. But the improbability of erosion on these satellites 
appears still stronger when we perceive the probability 
that they are mere watery globes, or at least completely 
covered by icy crusts. On such globes, though precipita- 
tions of inconceivable copiousness must have taken place, 
they occurred in an epoch before the formation of the icy 
crust. After its formation there would be no longer any 
rainy precipitation or erosive movements of waters. 

§ 2. PROGRESSIVE SUBSIDENCE OF TEMPERATURE. 

The nebular theory implies that all cosmical spheres 
after having attained the temperature due to condensation, 
begin a process of refrigeration due to excess of radiation 



PROGRESSIVE SUBSIDEN"CE OF TEMPERATURE. 459 

over amount of heat resulting from continued transforma- 
tion of mechanical energy. The consequences accom- 
panying the process of cooling have been traced from the 
nebular to the habitable stage; and incidental references 
have been made to more advanced stages. Let us con- 
template in a more orderly manner, some of the later inci- 
dents of cooling. So far as I have discovered, they reduce 
themselves to two categories. 

1. Shrinkage and Acceleration of Axial Motion. — The 
earlier relations of shinkage to rotary acceleration have 
heretofore come under consideration. But after a planet 
begins to be encrusted the method and the rate of refrige- 
ration are materially changed. In the fluid state, circu- 
latory convection brings the hottest portions continually 
to the surface, and the escape of heat by radiation is 
rapid. After a crust exists, the fluid within is protected 
from direct radiation. Its heat imparted to the crust must 
be conducted through to the exposed surface before it can 
be lost to the planet. As the crust thickens, the difficulty 
of conduction increases, and hence the rate of planetary 
cooling diminishes. At a certain time the temperature of 
the exterior ceases to be elevated by the heat reaching it 
from within, since the radiation quite equals the amount 
of heat conducted to the surface. With the progress of 
time, the superficial zone of fixed temperature, save from 
climatic influences, deepens. This zone experiences no 
contraction from its own cooling, but receives a lateral 
pressure arising from the general cooling and shrinkage of 
the planet. The consequences of this are thought by 
some to be manifest in plications, crushing, folds and 
mountain saliences. A convective movement of the inter- 
nal fluid, if any exists, may still be maintained, but it be- 
comes more and more sluggish as the crust thickens. 
With a planet as thickly encrusted as the earth, the escape 
of heat is extremely slow, and hence contraction and axial 



460 PLAlfETARY DECAY. 

acceleration are slow. Calculations based on the recorded 
dates of ancient eclipses indicate, as Laplace thought, that 
the terrestrial day has not been shortened within 2000 
years by more than a small fraction of a second. This^ 
however, if true, is no disproof of the existence of a shrink- 
age process. The proper acceleration may have been com- 
pensated by one or both of two causes. First, the equa- 
torial protuberance may have been prevented by the earth's 
rigidity from subsiding at such rate as to respond to the 
total shrinkage. The preservation of the equatorial diam- 
eter would largely conserve the rate of rotation. If the 
subsidence of the equatorial protuberance should proceed 
spasmodically, the irregularly varying oblateness of the 
earth might make itself felt in irregularities of the lunar 
motions and in the precession and other movements con- 
nected with terrestrial oblateness. The second cause com- 
pensating the effect of contraction is the influence of the 
tides, to which reference will shortly be made. 

If we had information concerning the actual tempera- 
ture of the earth's interior, it would be possible to calcu- 
late, under certain assumptions, the total amout of shrink- 
age which might result from any future refrigeration. 

2. Absorption of WcUer and Atniospliere. — I have 
already referred to the probably absorbed condition of the 
lunar ocean and atmosphere, and appended in a note the 
requisite formulae for ascertaining, the depth of crust de- 
manded for such absorption on any planet constituted 
with solids and fluids in the same proportion as the earth, 
when the value of certain constants has Hbeen ascertained 
by observation. The earth is the only planet on which 
observation enables us to ascertain directly the values of 
all the constants. Those accessible only to direct obser- 
vation are the following: 

(1.) The index of rock absorption by volume. By this 
is meant the volume of water absorbable by one volume of 



PROGRESSIVE SUBSIDENCE OF TEMPERATURE. 461 

the rocky crust of the earth. This can only be deter- 
mined by experiments on rock substances occurring near 
the earth's surface. Such experiments have been made 
by Durocher,* Hunt and others. f Two methods have 
been employed, one direct, the other indirect, or by infer- 
ence from the amount of condensation experienced in 
solidification or through hammering. Durocher experi- 
mented on those minerals which enter most commonly into 
the constitution of rocks, such as feldspars, micas, horn- 
blende and pyroxene. The minerals were reduced to 
coarse powder and exposed to moist air. The amount of 
water absorbed was found by weighings, and the results 
were as follows: The orthoclase of Utoe absorbed .0041 
parts by weight; seven other varieties of orthoclase ab- 
sorbed .0128 parts; thirty specimens of various minerals 
absorbed, on the average, .0127 parts. A large number 
of determinations of the absorptive properties of building 
stones was made by a committee of the British House of 
Commons and reported in 1839. This committee, of 
which the celebrated geologist Henry de la Beche was a 
member, employed blocks of an inch cube, which were 
thoroughly soaked in water under the receiver of an air 
pump, and subjected to the requisite weighings. The fol- 
lowing are some of the results reduced to absorption by 
volume: 

3 Silicious Limestones, .053, .085, .109. 

4 Nearly pure Limestones, .180, .206, .244, .310. 
4 Magnesian Limestones, .182, .239, .249, .267. 
6 Sandstones, .107, .112, .143, .156, .174, .221. 
Similar experiments were made by Professor T. Sterry 

Hunt on Canadian rocks, in 1864. J Dr. Hunt took small 

* Durocher, Bull. Soc. geol de France., II, x, 131. 

tSee a report on Building Stones made to the British House of Commons 
in 1839, by Barry, de la Beche and Smith. 

XT. S. Hunt, Amer. Jour. Set., II, xxxix, 183, March. 1865; Geology of 
Canada, 1865, 281^; Canadian Naturalist, February, 1865, 10; Chemical and 
Geological Essays, 164. 



462 PLAXETARY DECAY. 

broken fragments of the rocks — generally from 300 to 
600 grains in weight — carefully freed from adhering 
loose particles, dried them at 200° Fahr. until they ceased 
to lose weight; noted their dry weight, left them in con- 
tact with water for some hours, and then kept them im- 
mersed in water under the exhausted receiver of an air 
pump until all bubbles disappeared; removed them and 
wiped off superfluous water with blotting paper, and finally 
weighed them, first in air and then in water. These weigh- 
ings furnished the data for calculating, among other 
results, the index of absorption by volume. The results 
of these experiments on 39 varieties, mostly of stratified 
palaeozoic rocks, are published. A general view is given 
below: 

4 Potsdam Sandstones, hard and white, .0139 to .0272. 

2 Medina Sandstones, .0837 to .1006. 

3 Devonian Sandstones, .2024 to .2127. 

5 Shales, .0075 to .0794. 

6 Limestones, .0030 to .0527. 
11 Dolomites, .0215 to .1355. 

3 Tertiary Limestones, .2693 to .2954. 

Nearly all these experiments relate to the absorbent 
properties of stratified rocks, and the results cannot be 
taken as expressing the absorbent power of the cooled 
crystalline crust of the earth. Some extended experiments 
published by Dr. Hiram A. Cutting,* State Geologist of 
Vermont, include, among other rocks, 22 varieties of 
granite. His method of procedure was similar to that of 
Dr. Hunt. He used samples about three by four inches, 
and two inches thick. His specific gravities are those of 

*H. A. Cutting: Weight, Specific Gravity, Rates of Absorption and Capa- 
bilities of Standing Heat of Various Building Stones, Science, i. 254-6, Novem- 
ber 20, 1880. Dr. Cutting's results on the effects of heat possess great practi- 
cal interest. In this connection, consult also Gen. Q. A. Gilmore"s Report of 
the Compressive Strength, Specific Gravity and Ratio of Absorption of the Build- 
ing Stones of the United States, 8vo. 5T pp., 1876. 



PROGRESSIVE SUBSIDENCE OF TEMPERATURE. 463 

the particles of the rock or true specific gravity, and not 
of the gross bulk of the samples. The true specific gravi- 
ties of his samples range from 2.526 in a light-colored 
granite from Oak Hill, Maine, to 2.833 in a light-colored 
granite from Stanstead, Canada. The general mean is 
2.625. The absorption of one part, by weight, of water, 
required weights of granite ranging from 280 in a light- 
colored granite from St. Cloud, Minnesota, to 818 in a 
gray granite from Croton, Connecticut.* The mean ab- 
sorption was one part of water for 610 parts of rock by 
weight. The celebrated Quincy granite (syenite) stands 
near these means, having a specific gravity of 2.660 and 
an absorbent power expressed by 650. From these obser- 
vations it appears that the mean index of absorption by 
volume is .004303.t 

♦Thus the most absorbent granite was not the one with lowest specific 
gravity; nor the least absorbent, the one with highest specific gravity. This 
would result from the diSerent p7'oporttons of the lighter and heavier mineral 
constituents in the different granites. 

t As the mean amount of water absorbed by one part of granite is^^^y by 
weight, and the mean specific gravity of the granite is 2.625, the mean volume 
of water absorbed by one volume of granite is ^i X 2.625 = .004303 = i. 

We may readily deduce general formulae for the various results determina- 
ble from the weighings before mentioned. 
Let a = weight of dried rock. 

b = difference of weight^; of dried and saturated rock = weight of water 
which the rock is capable of absoi-bing. Represents the porosity of 
the rock. 
c = loss of weight in water, of saturated rock = weight of volume of water 
the same as the gross volume of the rock. Represents the gross vol- 
ume of the rock. 
Also c — b — weight of water displaced by net substance of the rock. 

Then - = specific gravity of the gross rock. 
= specific gravity of the net rock. 



c — b 
b 



= index of absorption by weight. 

Also, since volumes are directly as weights and inversely as specific gravities, 
. _ volume of water absorbed _ weight of water absorbed x sp. gr. of rock 
"" gross volume of rock. ~ weight of rock x spec. gr. of water. 

= — = - = index of absorption \>y volume. 

a 



464 PLANETARY DECAY. 

Attempts have been made by Bischof and MM. Charles 
Ste. Claire Deville * and Delesse f to obtain the difference 
of porosity of the same substances in the liquid and crys- 
talline states and thence to infer the absorbent properties. 
MM. Deville and Delesse showed that granite on fusion 
yields a glass having a density from .09 to .11 less than 
that of the granite. This means, supposing the gross 
volume to remain the same, that a granitic glass when 
crystallized increases the net specific gravity of its sub- 
stance, and must inclose pores in its structure to a corre- 
sponding extent; that is, to about one-tenth of its gross 
vojurae. Taking the mean density of granite at 2.625, it 
would, with such porosity, imbibe .03809 parts by weight 
for each part of granite. J On similar principles, Dr. 

The following forms are sometimes more convenient: 
Let s — weight of saturated rock. 

s' = weight of saturated rock in water. 
Then b - c — a: c = s — s' and c — & = a — s'. 

Whence = specific gravity of gross rock, 

; = specific o-ravitv of net rock, 

• )^ n 

-. index of absorption by weight, 
index of absorption by volume. 



s —s' 

* Deville, Com'ptes Renclus, 1845. 

t Delesse, Bulletin Soc. geol. de France^ 1847, IL xix, 64. 

X Some general expressions for converting such relations will often be found 

convenient. 

Let g — specific gravity of a rock, water being 1, 

m = weight of water absorbed by unit weight of rock, 

n = volume of water absorbed by unit volume of rock. 

Then mg = volume of water absorbed by unit weight of rock. 

Assuming unit weight of rock as unit volume of rock, 

n , n 

n = mg .•. in = -. and g — — 

Hence, further, by Weight, 

If rock is 1, water absorbed \< m. 

If water is 1.. rock absorbing it is — - -• 

And, by Volume, 

If rock is 1, water absorbed is n. 



PROGRESSIVE SUBSIDEITCE OF TEMPERATURE. 405 

Frankland has calculated that the moon in cooling through 
180° would create cellular space equal to 14,500,000 cubic 
miles.* In cooling throughout from a liquid to a solid 
state, supposing the liquid to be represented in density 
by the solid glass, the moon would acquire, according to 
the ratio of porosity found by Deville and Delesse, 528,- 
000,000 cubic miles of porous space, f 

Sagmann has pursued another indirect method for ob- 
taining the amount of porosity acquired in passing from 
the liquid to the solid state. He assumes that the poros- 
ity of the metals is due to molecular shrinkage experi- 
enced in coolings and that the condensation produced by 
hammering is the measure of such shrinkage. Calculating 
from the increased density of various metals produced by 
hammering, he finds that the porosity of cast iron is .075; 
nickel, .045; aluminium, .041; copper, .011; gold, .005. 
These results accord sufficiently well with those obtained 
by Deville and Delesse. 

It is doubtful whether these methods are suited for 
obtaining the absorbent properties of rocks. It is even 
highly probable that all liquefied substances diminish in 
specific gravity in the act of solidifying; though, as before 
stated, they may acquire, on further cooling, a density 
greater than that of the liquid magma. The assumed 
shrinkage which is supposed to create porosity is probably 
the normal shrinkage due to reduction of temperature con- 
siderably below the point of solidification. The porosity 
inferred is ten times as great as that indicated by direct 
experiments on absorption. M. S^Bmann's assumption also 
is quite gratuitous. At least, it affords no criterion of the 

If water is 1, rock absorbing it is - — — . 
n ing 

If ?i = .1, m = - = -A-. = .03809. 

* Frankland, Proc. Roy. Inst., iv, 175. 

1 1 TT X (1080)2 X .1 = 527,870,000 cubic miles. 

30 



466 PLANETARY DECAY. 

absorbent properties of the metals. This is shown not 
only by the want of any cited justification of the assump- 
tion, but by the fact that the result is ten times as great 
as direct experiment produces. 

It is safest, then to resort to direct experiment, and the 
index of absorption calculated from Dr. Cutting's weigh- 
ings must be regarded as the best present approximation 
to the absorbent power of the terrestrial crust. This is, 
i = 7i = .004303. 

(2.) The volume of the ocean. This depends on the 
superficial extent and the mean depth. The ratio of the 
total land surface of the earth to the total ocean surface 
is generally stated as 1 : 2.75. In other words, the land 
surface is represented by .267 and the ocean surface by 
.733. This is the ratio given in the Aomuaire for 1881, 
and the ratio here adopted. Herschel puts the ratio at 
1 : 2.86, since the total water surface is estimated at 146,- 
000,000 miles and the land surface at 51,000,000.* Profes- 
sor Haughton puts the area of the sea at 145,000,000 square 
miles, and the land at 52,000,000, which gives a ratio of 
1 : 2.79.t Dr. Carpenter adopts the ratio of 1 : 2. 78. J; 

The mean depth of the ocean can only be approximated. 
M. Saemann, in his paper already quoted, assumes it as 
600 metres, or 1,968 feet, which is a manifest underesti- 
mate. The results of the Challenger and earlier soundings 
combined together, give for the mean depth of the North 
Atlantic, about 2,600 fathoms; for the South Atlantic, 
about 1,900 fathoms; for the equatorial Atlantic, 2,000 
fathoms, making for the general mean of the Atlantic, 
2,166 fathoms.§ The mean depth of the Pacific between 

''Herschel: Physical Geography . 2d ed, 19. 

t Haughton, Proc. Boy. Soc, vol. 26, p. 53, 1877. 

tW. B. Carpenter, Encyc. Brit., Art. ''Atlantic Ocean." 

§ This was written before learning Sir Wyville Thomson's estimate as stated 
in his Rede lecture at Cambridge in 1877. He makes the mean depth of the At- 
lantic about 2,500 fathoms, and this opinion is probably as near the truth as we 
can come. 



PROGRESSIVE SUBSIDENCE OF TEMPERATURE. 467 

Japan and San Francisco, according to the calculations of 
the United States Coast Survey, based on the transmission 
of an earthquake sea wave, is 2,300 fathoms. Calling 
this the mean depth of the Pacific, and giving the number 
equal weight with that for the depth of the Atlantic, as 
found above, the mean depth of the two is 2,233 fathoms, 
or 12,398 feet, or 2.538 miles, which may be provisionally 
assumed as the mean depth of the general ocean. This is 
6.8 times as deep as assumed by M. Saemann. 

(3.) Calculation of absorptive capacity of the plane'.ary 
pores. Haviug the area and mean depth of the ocean, we 
may ascertain its cubic contents; then, knowing the index 
of absorption of the earth's crust, a simple application of 
the general formula before deduced (p. 382) gives the 
thickness of cooled crust requisite to effect the absorption 
of the ocean. Many circumstances may render the absorb- 
ent property of the deep crust different from that of sur- 
face rocks. Any residual heat above the temperature at 
which experiments have been made would probably dimin- 
ish the power of absorption. On the contrary, great con- 
densation of the water might take place, either through 
the physical action of minute pores, or the great pressure 
of superincumbent matter. In the present state of knowl- 
edge, we can only assume that the absorbent property of 
the crust is about that of the superficial rocks. Employ- 
ing the index of absorption given by Dr. Cutting's experi- 
ments, and neglecting the superficial zone already satu- 
rated with water, our formula gives 490.8 miles as the 
thickness of the terrestrial zone, which would retire all the 
water now filling the ocean's basin. If we wish to know 
what thickness of zone below the zone already saturated 
would suffice to absorb the ocean, we may employ first the 
formula given for obtaining the thickness of the saturated 
zone. In this, if we assume the rate of increase of tem- 
perature downward to be one degree for 50 feet; the 



■468 PLAJ5"ETARY DECAY. 

mean temperature at the surface, 47°; the temperature at 
which water vaporizes in the crust of the earth, 212° 
Fahr., and the depth to constant temperature, 80 feet, the 
saturated zone is shown to be 8,330 feet or 1.5776 mile. 
Employing this value in the general formula, we find that 
a zone 491.42 miles thick within the present saturated zone 
would absorb the ocean's water. 

According to M. S^mann's calculations, the pores of 
the rocks of the totally refrigerated earth, after having 
taken in the waters of the ocean, would amply suffice for 
the absorption of the atmosphere also. But I have shown 
that he has assumed a depth for the ocean which is over 
eight times too small, and, on the contrar}^, an absorbent 
property of surface rocks which is ten times too great. 
Accordingly, it does not appear that this porosity is suffi- 
cient for the total retirement of the water and air. 
Taking Sir John Herschel's mass of the atmosphere (re- 
duced to surface density, yg^ooooo)? ^^^ relative volume is 
.003837; and application of the formula adapted to this 
case (p. 383, note) shows that this is more than the 
capacity of the pores would receive after the absorption 
of the ocean. This is evident, indeed, from the fact that 
the ocean would appropriate .3276 of the earth's total 
capacity, leaving only 2.052 times this amount unappro- 
priated, while the relative volume of the ocean being 
.001409, the relative volume of the atmosphere (.008837) 
is 2.723 times that of the ocean. It is entirely probable, 
however, that absorbed air would undergo a sufficient con- 
densation to render the whole atmosphere absorbable. 
Supposing a somewhat free communication among the 
pores, columns of air would exist reaching from the zone 
of the absorbed water to the earth's surface, which would 
be 1,230 miles. Now the whole depth of the atmosphere 
reduced to density of surface air would be but five miles. 
At half the depth of the zone left unoccupied by the 



PROGRESSIVE SUBSIDENCE OF TEMPERATURE. 469 

ocean — that is, at 615 miles — there would exist, making 
no allowance for diminished gravity below the surface, a 
pressure of 123 atmospheres, which would condense the 
air into 123 times less than its surface volume. If any- 
thing should interfere with the application of Mariotte's 
law, it would be an attraction for the air which would 
produce an equal or greater effect; as in the case of the 
condensive absorption exerted by charcoal, platinum- 
sponge and some meteoric stones. This method of cal- 
culation, however, assumes erroneously that each addi- 
tional five miles of depth adds one atmosphere to the 
pressure. But as gravity beneath the surface of the earth 
varies a^ the distance from the centre, the pressure at the 
bottom of 615 miles would be only 104 atmospheres, and 
at the depth of 1,230 miles, 208 atmospheres.* There can 
be no doubt, consequently, after this correction, that the 
condensation would be sufficient, and much more than 
sufficient, to permit the final withdrawal of the terrestrial 
ocean and atmosphere. 

As to the remoteness of the epoch when the earth's 
water and atmosphere will have been absorbed, little can 

*Let r be the earth's radius and 5 a; be the depth beneath the surface, then 

the pressure due to successive five-mile zones will be expressed in terms of one 

atmosphere, as follows : 

r — 5 r — 5x2 r— 5X3 r — 5 x 4 r — hx 

1 J J J . 

r r r r r 

The last term expresses the pressure due to the last five miles. The pressure 

f -§■ 2; 

due to the middle five miles is f^ — , and this is the mean pressure in the 

whole series of zones. 

If 5 a? :;= 1,230 miles, the mid pressure is 
3%3 — 615 



3963 
The pressure due to the lowest five-mile zone is 
3963 — 12.30 



844 atmos. = mean pressure, 
e zone is 
689 atmosphere. 



3963 
The total pressure at the bottom is 

^ X .844= 207.624 atmospheres, 

and the pressure at the bottom of a column half as high is half as great. 



470 PLANETARY DECAY. 

be said. In Mars we have a planet whose terrestrial 
stage, according to our theory, would have been reached 
9,500,000 years ago, if we suppose its incrustation to have 
begun when the earth's began, and use the table of time 
ratios heretofore given. Since that epoch Mars has con- 
tinued to advance in its evolution at a rate two and a half 
times as rapid as the earth, and yet Mars has not attained 
the stage of complete atmospheric absorption.* That is, 
if the evolution of the earth can be compared with that 
of Mars, it will be more than 24,000,000 years before the 
earth's atmosphere is absorbed. And to this must be 
added the difference in age of the two planets. On the 
other hand, assuming the Same time ratios as before, we 
may reason from the condition of the moon, and, adopting 
14,000,000 years as the earth's incrusted age, the moon 
reached the terrestrial condition 11,666,666 years ago. 
The advance of the moon in its evolution since that 
epoch is equal to the advance to be made by the earth in 
70,000,000 years. But the moon's atmosphere is absorbed, 
and hence within 70,000,000 years the absorption of the 
terrestrial atmosphere will be effected. That is, reasoning 
from the slender data within reach, the absorption of the 
earth's atmosphere will be effected in a period lying 
between 24,000,000 and 70,000,000 years. 

The secular disappearance of the surface waters of the 

*It will be noticed that all the calculations made in reference to the absorp- 
tion of planetary water and air assume a planetary density equal to the mean 
density of granite (2.625). But the deeper portion of the earth has a much 
higher density, and hence, probably, possesses a lower index of absorption, and 
would not, consequently, be able to effect all the absorption attributed to it in 
the text. Similarly, the moon, though its density is only .607 compared with 
earth, exceeds granite in density, and would have a lower absorptive capacity 
than we have attributed to it. Mars, also, with a mean density (.6481) a little 
greater, Is more dense than granite, and with a presumably larger proportion of 
water and air, might be supposed incapable of completely absorbing its surface 
fluids: so that, after all possible absorption is effected, a residual portion of 
the Martial atmosphere (if not of water) will remain permanently. This con- 
sideration bears on the inferior limit of time within which the earth's atmos- 
phere may be absorbed. That is, it may not be "more than 24,000,(X)0 years."' 



PROGBESSIVE SUBSIDEiq^CE OF TEMPERATURE. 471 

earth is a fact of observation arid record. The ocean was 
once universal; it is in our times withdrawn from three- 
tenths of the earth's surface. This is generally attributed 
to the progressive increase of the inequalities of the ter- 
restrial surface; and it is not possible to disprove the posi- 
tion. But there are many indications of a slow desicca- 
tion of the land during human occupation. Lakes have 
disappeared or diminished; marshes and alluvial areas 
occupy situations once water-covered. Climates have be- 
come more arid; and many regions once productive have 
become sterile and uninhabitable. Numerous illustrations 
of these statements are familiar to every intelligent per- 
son. I have been accustomed for fifteen years to discuss 
the subject in my university lectures. No one, however, 
has given the facts so much consideration as Professor J. 
D. Whitney; and after directing the attention of the 
reader to the interesting phenomenon, I must refer him for 
the abundant facts, to Professor Whitney's writings.* 

To the present probable condition of the moon I have 
had frequent occasion to allude. That its surface is desti- 
tute of air and water is generally admitted. M. Faye main- 
tains that these fluids were never present; but it is impos- 
sible to adopt any theory of the origin of the moon by 
derivation from the earth or from a common mass with the 
earth, and deny the necessity of aqueous and atmospheric 

* J. D. Whitney: American Naturalist^ x. 513, September, 1876; Memoirs, 
Museum of Comparative Zoology, Cambridge, Vol. vii. On Climatic Changes of 
Later Geological Times, Part I, 120 pp., 1880; Part II, 121-264 pp., 1882, Part III, 
265-394- pp., 1883. See also Amer.Jour. ScL, III, xx, 460, xxiii, 489-90, xxv, 153. 
For some shrinkages of American lalies, see King: Geology of the kOth Paral- 
lel, i, 490-504; Stevenson, in Wheeler's Report, iii, 453-71; Howell, ib., 250-1; 
Hayden, Report on Wyoming, 1870, 72-3 and Annual Report for 1874, 48; Pacific 
R. R. Report, ii, 97; Endlich, Hayden Report, 1875, 147-8; Nature, xxii, 41; A. 
R. C. Selwyn: Geol. of Canada, 1873-4, 27, 58; C. Robb: Geol. of Canada, 1874-5, 
53-6. Compare also, A. Winchell, Trans. Mich. Agric. Soc,, 1865; Syllabus of a 
Course of Lectures on Geology, 1869, 7, ib.. 1870, 12; ib., 1874, 20, 24: ib., 1879, 44, 
112; Amer. Jour. Sci., II, xxxviii. November, 1864; Sketches of Creation, 1870, 
237-9. 



472 PLANETARY DECAY. 

constituents. The apparent absence of such fluids can only 
be explained on the theory of their complete absorption. 

By the logic of our theory we are constrained to believe 
that Avater and air have disappeared from the surface of 
every body in our system, of greater age than the inoon, 
and not much surpassing it in size, provided its solids and 
liquids were originally proportioned somewhat as in the 
moon and earth. But according to our theory also, all 
the older bodies must have received a larger proportion of 
fluids than the earth. The water surface of Mars must 
have been in larger ratio than on the earth, and the Mar- 
tial atmosphere must have been more voluminous. Then, 
perhaps, Mars might become completely refrigerated with- 
out absorbing all its water. Still more likely, a surplus of 
atmosphere would remain. That a full supply of water 
and air is not present is manifest from the comparatively 
unclouded condition of the disc of the planet. In this 
view, the indications of an atmosphere will never disap- 
pear from Mars. It may have been senescent and refrig- 
erated for millions of years — as indeed our moon may 
have been. As to the Martial satellites, it cannot be 
doubted that they have long since attained their final con- 
dition, so far as concerns heat and absorption of fluids; 
and that cannot be far different from the condition of 
their primary. 

The asteroids should present a still further divergence 
from the conditions of the earth. They are probably ice- 
covered and frozen to the core, each retaining an abundant 
quota of atmosphere. 

Jupiter, I have assumed, in consequence of his enor- 
mous mass, to be still far short of the terrestrial stage. 
The large percentage of fluids in his constitution renders 
it improbable that any considerable land surface should 
ever emerge; and still more improbable that the fluids 
should ever become completely absorbed. Jupiter's glacier- 



SYNCHRONISTIC MOTIONS AND TIDAL FINALITIES. 473 

clad satellites present the picture of Jupiter's remote future 
destiny. 

In the ultra-Jovian planets this destiny is attained. All 
fluid absorption of which they are susceptible is a finality 
long since attained in each of the three successively. They 
are globes of solid ice, inclosing cores of rocky material, and 
wrapped in vapor-laden atmospheres. (See chapter iii, § 6.) 

Looking in the other direction, it may be suggested 
that Venus and Mercury, in consequence of their dimin- 
ished proportion of fluids, will become desiccated and air- 
less at a relatively earlier age than the earth. That they 
are not yet so is indicated by the envelopes of vapor which 
conceal their discs from view. 

§ 3. SYNCHRONISTIC MOTIONS AND TIDAL FINALITIES. 

It appears that tidal influences have performed a part 
of prime importance in the evolution of worlds. I have 
had former occasion to explain these influences upon the 
rotation of cosmic bodies, and have pointed out the tidal 
interactions of the earth and moon and of the sun and 
planets. The subject comes again into view in connection 
with the ulterior vicissitudes of planetary bodies which we 
are now grouping in a connected presentation. 

Directing our attention first to the interactions in which 
the earth is concerned, we perceive that the tidal retarda- 
tion which it is destined to experience will first bring 
about synchronism between the day and the lunation. 
The earth and moon will turn permanently the same sides 
toward each other, and the two will rotate as parts of a 
rigid system about a common axis. The reaction of the 
earth upon the moon will have caused it to recede to the 
distance of about 347,100 miles, and the lunation will, 
accordingly, have been lengthened to 48.3G days,* 

♦Thomson and Tait: Treatise on Natural Philosophy, 2d ed. §276. The tidal 
retardation of the earth's rotation was first suggested by Kant, in 1754. 



474 PLANETARY DECAY. 

The tidal retardation of the earth's rotation, that is, 
the gradual lengthening of the day, is a fact of observa- 
tion. The number of seconds since the occurrence of an 
ancient eclipse, for instance, would be somewhat less than 
calculation shows, if the day, and hence the second, has 
been slowly lengthened. The subject was investigated by 
Laplace, on the basis of eclipse observations recorded by 
Hipparchus, 720 B.C., and shows that the length of the 
day had not increased one ten-millionth of itself, or y^ of 
a second, in the intervening time. Bat Adams, in 1859, 
pointed out an oversight in the investigation of Laplace 
on the acceleration of the moon's mean motion, showing 
that one-half of its apparent acceleration, relatively to 
the angular velocity of the earth's rotation, remained un- 
explained. That is, the moon was 5". 7 in advance of the 
position she would have relatively to a meridian on the 
earth at the end of a century, after all known disturbing 
causes had been taken into account. This is the same in 
effect as if the earth in her rotary motion were a little be- 
hind, and Delaunay soon showed that this was probably 
the true explanation. Investigating the amount of tidal 
retardation of the earth's axial velocity due to the influence 
of both sun and moon, and allowing for the retardation of 
the moon by reaction of the lunar tide, he found that the 
earth's meridian was behind the position required by the 
lunar motion, by just about the amount of the tidal retard- 
ation. Thus it appears that the terrestial day is shortened 
about twenty-two seconds in a century, and tidal action 
is the cause.* Should this rate of retardation continue, and 
should the length of a lunation not change, a state of syn- 
chronism would be attained in about 378,000 years. But 
the rate will be diminished, both by the slow recession of 
the moon and by the growing infrequency of the tide. 

*But oil the contrary, seeE. J. Stone, Proc.Roy. Soc.,A.\>t. 12, 1883, Nature, 
xxviii, 71. 



SYNCHKONISTIC MOTIONS AND TIDAL FINALITIES. 475 

The length of the lunation will also be gradually in- 
creased. 

After a state of lunar-terrestrial synchronism shall have 
been attained, it cannot remain undisturbed through the in- 
definite future. The solar tide still exists, though it recurs 
only once in forty-eight days, with the antitide intervening. 
This tide also lags, and the sun's action upon it yields a tan- 
gential component against the rotation of the earth, tend- 
ing to reduce the earth's rotary motion below the rate of 
the moon's orbital motion. That is, in course of time, the 
lunar tide, instead of being ahead of the moon's posi- 
tion, will be behind it, and the moon and sun will contend 
for the control of the earth's rotation. The sun will strive 
to lengthen the day and the moon will now strive to shorten 
it. The reaction of the lunar tide will now retard the 
moon's motion, and centripetal force will gain a slight 
ascendancy. As a consequence, the moon will approach 
the earth and will ultimately be precipitated upon it. 

Meantime, the tidal interactions between the earth and 
sun repeat those between the moon and earth. The lag- 
ging of the terrestrial tide on the sun, acted on by the 
earth, tends to equalize the sun's rotation and the earth's 
revolution. The reaction of this tide on the earth's motion 
increases the distance between the earth and sun, and the 
lagging solar tide on the earth, acted on by the sun, con- 
tinually diminishes the rotary velocity of the earth, and 
(through the displacement of the lunar tidal protuberance) 
the orbital velocity of the moon, thus accelerating the 
precipitation of the moon on the earth. As an outcome 
of this contest between the moon and sun, if I reason 
correctly, the day Avill become a little longer than the 
lunation, so that the lunar tidal protuberance will exist 
continually a little behind the moon's position, and the 
solar tidal protuberance a little ahead of the sun's posi- 
tion, so placed that the accelerating influence of the moon 



476 PLAKETARY DECAY, 

will be exactly balanced by the retarding influence of the 
sun. Thus the moon will perpetually approach the earth, 
and the earth will perpetually recede from the sun. But 
when eventually the moon falls to the earth, the solar tide 
will bring the latter to such a rate of rotation that the 
day will equal the (lengthened) year; and with no further 
interferences, this state of rotation would continue forever. 

If we consider the ultimate tidal history of Venus, it is 
manifest, on grounds before explained, that so long as 
fluids exist on the surface of the planet, or so long as a 
state of incomplete rigidity remains, a solar tide will exist, 
whose lagging must furnish the condition of a tangential 
component opposing axial rotation. Venus will therefore 
be reduced to a state of synchronism, and will revolve at 
an increased distance from the sun. Simultaneously the 
tide raised on the solar surface will offer the conditions of 
solar rotary retardation, and neglecting the influence of 
other planets, Venus and the sun will finally rotate as a 
rigid system around their common centre of inertia. The 
tidal influence of Venus upon the sun is two and a third 
times as great as that of the earth; hence the sun will obey 
Venus at first, and arrive at synchronism with that planet. 
Then, as the rotary velocity of Sun- Venus will exceed the 
orbital velocity of the earth, the geal tide raised on the 
sun will be in advance of the line joining the centres of 
tlie earth and sun, so that the tangential component of the 
earth's action on the solar geal tide will be retardative, 
and the sun will tend toward synchronism with the earth. 
The sun's tidal reaction on Venus will now, be retardative^ 
and Venus will approach the sun. The remote tidal inter- 
action with Mercury will be similar. It may be noted also 
that the tidal control exerted by that planet over the rota- 
tion of the sun will be to that exerted by the earth as 
1.118 to 1. 

There is ground for believing that the rotary motions 



INFLUENCE OF INTERPLANETARY RESISTANCES. 477 

of all the satellites of our system have long since become 
synchronistic with their orbital motions. In a system em- 
bracing numerous moons, like Jupiter's, each satellite pro- 
duces its separate and independent effect, and these are 
always concurrently retardative. In some distant age the 
rotation of the planet will become coincident with the 
revolution of the nearest satellite. The retardative action 
of this will then cease, and the retardation will continue 
under the influence of the other satellites, toward the at- 
tainment of synchronism with the second satellite. But 
meantime the first satellite has a greater angular velocity 
than the planet, and the relation of Phobos to Mars is 
realized. It tends now to accelerate the rotation of the 
planet. The reaction of the planetary tide on this sat- 
ellite retards its motion, and brings it on a course of pre- 
cipitation in a spiral path upon the planet. At length, 
synchronism with the second satellite is attained, and its 
history repeats the history of the first. Ultimately, all the 
satellites except the Ifist are precipitated on the primary, 
and the planet's rotation attains synchronism with its 
revolution. Theoretically the sun must be viewed as still 
further retarding the planet's rotation by action on the 
lagging solar tide; and this tide reacting on the last satel- 
lite, retards it and accomplishes precipitation on the planet. 
Finally, disregarding the presence of other planets, this 
planet and the sun attain synchronistic motions, as in the 
case of the earth-sun. The tidal action of the sun, how- 
ever, upon the major planets is so slight relatively that the 
events contemplated are removed to a future excessively 
remote, and we may fairly expect them to be forestalled 
by other eventualities. 

§ 4. ULTIMATE INFLUENCE OF INTERPLANETARY RE- 
SISTANCES. 

The analogies of nature and the ascertained facts? of physical science for- 
bid us to doubt that every one of them — every star and every body of every 



478 PLAXETARY DECAY. 

kind, moving in any part of space — has its relative motion impeded by the 
air, gas, vapor, medium, or whatever we choose to call the substance occupying 
the space immediately round it.— Sir W. Thomson and P. G. Tait. 

It is a common remark that Laplace found the harmony 
of the solar system stable, provided that interplanetary 
space is a vacuum, and the planets themselves are per- 
fectly rigid bodies. More recent science has shown that 
neither of these conditions of indefinite stability exists. 
Occasions have arisen in other connections, to point out 
many of the facts which contravene the conditions of 
stability, but it will be useful to summarize in due connec- 
tion the indications of eventual conglomeration around 
centres of orbital motion. Were the planets all as solid 
as granite, there would exist sufficient plasticity to yield 
a tidal protuberance under their mutual actions and that 
of the sun. It was shown in the last section that tidal 
actions and interactions affect both rotary and orbital mo- 
tions; and that under certain circumstances, mere tides 
tend to precipitate planetary masses upon their centres of 
motion. The freer the mobility of certain parts of a tide- 
bearing body, the more efficient this action, provided some 
of the other parts are relatively much more rigid, to fur- 
nish points of resistance to the parts tidally moved. But 
probably no matter exists so completely rigid as not to 
undergo relative displacement in the presence of the tre- 
mendous forces exerted by planetary and solar masses. 
Hence, on planets not covered by w^aters, and on planets 
whose seas have been converted into ice, tidal action con- 
tinues, and tidal finalities are impending. Such results 
flow from the absence of complete planetar}^ rigidity. 

A more commonly recognized cause of a tendency 
toward central precipitation is the presence of resisting or 
colliding matter in the interplanetary spaces. In another 
connection * I have discussed the diffusion of meteoroidal 

* Especially in Part I, ch. i, § 6. 



INFLUENCE OF INTERPLANETARY RESISTANCES. 479 

matters and of other possible forms of matter consisting of 
gases, vapors or ethers, and have reached the conclusion 
that space is so far from the condition of a vacuum that it 
seems rather to be a plenum, the contents of which neces- 
sarily interfere with all relative motions in the universe. 
The conception of an extremely attenuated material me- 
dium has been entertained ever since the time of Sir Isaac 
Newton, and many eminent authorities have felt great 
confidence in its reality, and have discussed its necessary 
properties — sometimes holding it to be a continuous fluid, 
and in other cases considering it rather to have an atomic 
or discrete constitution.* It is impossible that an ethereal 
medium, however tenuous, should exist without impressing 
results on the motions of cosmical bodies. This influence 
has been thought detected in the accelerated angular 
velocities of Encke's and Winnecke's comets, particularly 
the former, which moves throughout its whole course in 
an orbit relatively not remote from the sun. The ethereal 
medium is generally assumed to diminish in intensity with 
increase of distance from the sun. The assumption that 
the density varies inversely as the square of the distance 
agrees best with observation on the cometary effects of 
supposed ethereal action. The formulae expressing these 
perturbative effects show that the tendency of the medium, 
conjointly with solar attraction, would be to continually 
accelerate the mean motion and diminish the eccentricity 
of the orbit. Accelerated motion arises from diminished 
distance from the sun. If these conclusions are correctly 
based, we are therefore enabled to make actual observa- 
tion of the slow spiral approach of a body toward its cen- 
tre of motion. It must be said, however, that the later 
movements of Encke's comet do not clearly sustain the 
theory of slow precipitation, and some high physical au- 

* We might add to the citations heretefoie made (p. 52) Kretz : Matiere et 
Ether; indication d'une methode pour etablir les proprietes de I' Ether. 



480 PLANETARY DECAY. 

thorities deny that its entire observed history favors the 
doctrine of precipitation, or lends any distinct evidence of 
the existence of a resisting medium.* If, however, the 
earlier and later observed movements reveal irregulari- 
ties in the motion of the comet which cannot be ascribed 
to planetary perturbations, it is allowable to suspect that 
the temporary and unknown cause of irregularities will 
hereafter cease to act, and the subsequent accelerated 
motion of the comet reveal with increased distinctness the 
presence of a resisting medium. But whether human skill, 
in the course of one or two generations, shall succeed or 
not in discovering the effects of a resisting medium, we 
must admit that the effects are real, or incur all the 
embarrassment of ignoring the existence of any vibratory 
medium for transmitting the radiations of the sun and 
other heavenly bodies. If we admit, even in theory, the 
existence of a universal material fluid, we must admit, as 
a consequence, the ultimate precipitation of the planetary 
bodies upon their centres of motion. 

I have heretofore expressed the opinion that another 
cause exists in space adequate to exert the resisting action 
generally ascribed to the ethereal medium. That cause is 
meteoroidal. It is easy to conceive that a perturbation 
proceeding from this cause would produce a mean effect 
equivalent to that of a resisting force acting in the tan- 
gent to the instantaneous orbit; and that the amount of 
the perturbation or resistance should increase as the dis- 
tance from the sun diminishes. It seems to me that a 
disturbance of this nature is more clearly established than 
the resisting property of the ethereal fluid. 

* Dr. Backliiud, of Pulkowa. conclude:? from an investigation of the motion 
of Encke".s comet that '• if there exists a tangential force which varies ^vith the 
dimensions of the comefs orbit, its effect is not only secular but periodic." 
His investigation proves that the acceleration of the mean motion m the period 
1871-81 was less than half the value found by Encke and Asten for the period 
1819-65 {Nature, xxviii, 181). This is the latest announcement on the subject. 



Il^FLUEKCE OF INTERPLANETARY RESISTANCES. 481 

Many trains of investigation lead toward the convic- 
tion that space is pervaded by some condition of matter 
in a state of general dissemination. The intimation has 
recently come to us through the researches of Captain 
Abney, that the vapor of water and hydrocarbon com- 
pounds are possessed of a general distribution. The 
latter, at least, had been already detected in comets and 
in meteoric stones. It is equally probable that hydrogen 
helps to fill the void between us and the sun; and no 
improbability is apparent that the very atmosphere which 
we breathe stretches on indefinitely toward the stars, 
diminishing ever in density as we recede from the earth, 
but increasing in density as we approach other bodies, 
and constituting an intelligible material intermedium. 
One can imagine what extreme tenuity such a medium 
must possess in the interplanetary spaces when it is con- 
sidered that the meteoroids moving through it at the rate of 
forty miles a second do not develop heat more rapidly than 
the power of radiation in the regions which they traverse 
is capable of conveying it aw^ay. 

By some cause acting after the manner of a resisting 
medium certain comets seem to have been impressed. By 
such a cause the satellite Phobos may have been im- 
pressed, for it appears to be in actual course of precipita- 
tion. By some similar cause or causes all the planets 
and satellites must be slowly affected; and our inability 
to discern and measure the results may be well ascribed 
to their minuteness within human periods, and the effect 
of other perturbative causes in disguising them. It ap- 
pears to be generally admitted that precipitative tenden- 
cies exist, and none of the eventualities of the distant 
future will be able to annul them. We therefore conceive 
of the ultimate return of the various members of the 
sun's family back to the central mass from which they 
originally sprang. 
"^31 



482 PLAKETAEY DECAY. 

We observe in the Solar System a mode of action 
^yhich in principle is the same as that of interplanetary 
matter; but the action is exerted by matter which consti- 
tutes a part of the aggregation acted upon. It exists in 
cometary and meteoroidal trains, in the rings of Saturn, 
and probably in the zodiacal light — possibly, also, in the 
swarm of asteroids and in other groupings of cosmical 
particles and masses. It is not conceivable that the parts 
which constitute the head or even the tail of a comet, for 
instance, stones, grains, dust, vapors, move with such uni- 
form velocities and directions as not to collide with each 
other. I have heretofore, following Sir William Thom- 
son, ascribed the evidences of a gaseous glow in the head 
of a comet to the collisions of the stony constituents of 
which it is composed. Where mean velocities are fifty or 
one hundred miles a second, it requires but slight differ- 
ences of velocity to produce relative velocities equal to 
those of military projectiles. A cannon ball moves 1,400 
to 2,000 feet in a second, and yet its impact upon a solid 
body always develops a flash of light. But this velocity 
is mere rest when compared with that of a comet in its 
flight. Now, in case of these mutual collisions among 
the parts of a comet, the velocities of some will be accel- 
erated and those of others retarded. Those retarded are 
liable, of course, to be accelerated again by other colli- 
sions, so that the total amount of motion in the assem- 
blage should remain constant, so far as actions in the 
system are concerned. Nevertheless, the changed velocity 
of a part results in a changed intensity ,pf action from 
without. Retardation results in an increase of centrip- 
etal tendency, while acceleration results in an increase of 
centrifugal tendency. The accelerated and retarded parts, 
therefore, tend to separate from each other, and thus 
coming into changed relations to an external action, are 
further separated. In the nearer proximity of a great 



INFLUEI^CE OF I^-TEEPLANETAEY RESISTANCES. 483 

attractive mass, as when a comet passes near a planet, 
these changed relative distances of the cometary parts 
from the mass enable the latter to v^rrench the comet's 
constitution to a destructive extent. The effect is an 
incipient disintegration — a dispersion of the parts and 
the commencement of their precipitation upon the dis- 
turbing body. The meteoroidal stage of a comet's life 
exemplifies the progress of the disintegration; and the 
meteoroidal swarm itself must be regarded as going to 
pieces through the continuance of these internal and 
external actions. 

As the rings of Saturn are probably mere cosmical 
atomSj quite as hard and discrete as those existing in 
comets and meteoroidal swarms, there is equal reason to 
suppose them also subject to mutual collisions. In such 
case, the parts suffering retardation would approach the 
planet and circulate with restored and even increased 
velocity, in nearer proximity to it. Thus certain particles 
of the Saturnian rings should continually transfer them- 
selves from other regions to the inner margin of the ring 
system. The ring system should slowly, molecularly, grow 
inward and should ultimately come into contact with the 
planet. Now it is interesting to know that Otto Struve, 
in 1851, arrived at the identical conclusion that *'the inner 
edge of the Saturnian ring was gradually approaching the 
planet, the whole ring spreading inward, and making the 
central opening smaller." This conclusion was based on 
the descriptions and drawings of astronomers of the sev- 
enteenth century, and especially of Huygens.* 

* Struve, however, has lately reported the results of new measuremeuts made 
in 1882, from which it appears that the inner diameter of the ring though slightly- 
shorter than in 1851, is less shortened than his theory requires. The space, how- 
ever, which in 1851 separated the inner or dark ring from the bright one is now 
closed up, and the dark ring seems to be merely a faint continuation of the 
bright ring.— x4s^/ on. Nachrichten, No. 2948. On these rings I cite further, G. 
A. Hirn: Memoire sur les conditions oTequilibre et sur la nature probable des 
anneaux de Saturn, 1872; and Le Monde de Saturn, ses conditions d'existence et 
de duree, 1872. 



484 PLANETARY DECAY. 

If the " zodiacal light," as coirimonly supposed, is caused 
by sunlight reflected from an assemblage consisting of 
myriads of solid masses of matter, then a similar action 
must take place among them, and the assemblage must 
gradually spread itself in the plane of its orbit toward the 
sun. These interactions would thus conspire with the 
actions of other interplanetary matter in supplying a con- 
tinuous descent of meteoroidal substances upon the body 
of the sun. 

If the asteroidal group is, as some suppose, sufficiently 
numerous to create the probability of frequent collisions, 
then the slow extension of this group sunward over the 
plane of the mean orbit is a contingency not to be over- 
looked. 

§ 5. GENERAL REFRIGERATION. 

1. Planetary Refrigeration. — This is also one of the 
eventualities of a planet's lifetime, and one which has 
again and again been brought before our attention. We 
see this state exemplified in the condition of our satellite, 
and we believe it has been attained in the satellites of 
other planets, and even the older of the planets them- 
selves. We have traced the slow processes of planetary 
desiccation and atmospheric absorption in those planets 
which belong to the earth group, and have discovered the 
cause of the perpetual presence of watery vapor and an 
atmosphere in other planets probably long since frozen to 
the core. We recognize the refrigerated state as an 
ulterior stage in all planetary life. 

2. Solar Refrigeration. — But it may not be fully ap- 
preciated that, as the bodies now planets were once suns, 
so the bodies now suns are destined to be planets. Even 
the long-enduring sun of our system is destined to be ex- 
hausted. I entertain the opinion that most of the heat 
by which the sun now maintains the activities of his em- 



GENERAL REFRIGERATION^. 485 

pire is a portion of the primordial heat evolved in the 
original aggregation of nebular masses and their progres- 
sive condensation. Mucli heat, undoubtedly, has been 
evolved by later contraction during the periods of plane- 
tary history. This process has greatly retarded the lower- 
ing of the solar temperature. But the sun has always 
been cooling, and the reason why his temperature is still 
so high is simply the vastness of his mass. Whatever ac- 
cessions of heat may arise from further contraction, or 
from meteoric or planetary precipitations, will serve only 
to eke out the original supply. These are indeed neces- 
sary inferences from the cosmic theory set forth in the 
present volume ; but they are also conclusions from inde- 
pendent considerations. Let us glance at some of the data. 

(1.) Inductive Evidences of Seculcir Lowering of Ter- 
restrial and Solar Temperatures. — (a) In Historic Times. 
— Very much discussion has taken place on the question 
whether human observations have established any changes 
in the mean temperature of terrestrial climates. It is not 
necessary here to cite the various facts and opinions, but 
it is important to reproduce the conclusion reached by 
Professor J. D. Whitney, who has given the whole subject 
a thorough and patient examination.* He says: "There 
is evidence very considerable in amount and importance, 
to the effect that a decrease in temperature during historic 
times has manifested itself in various ways besides desic- 
cation." 

{h) In Prehistoric Times — No aspect of the palagon- 
tological relics of former periods is less questionable than 
their testimony to the secular abatement of terrestrial 
temperature. It is not necessary here to make particular 
citations of facts, since they are recorded in all manuals 

*J, D.Whitney: The Climatic Changes of Later Geological limes, 4to., 
394 pp., especially 219-41. From the Memoirs of the Museum of Comparative 
Zoology, Cambridge, Vol. vii. See, also, C. Konig, Kosmos, viii, 283-91. 



486 PLANETAEY DECAY. 

of geological science. The plants, especially, which 
clothed the lands of the temperate and arctic zones in 
earlier times, find their modern allies in forms restricted 
to warmer climates and to lower latitudes than their pro- 
totypes.* The evidences, also, of a persistent process of 
desiccation of the continents during Post-Tertiary time, so 
industriously accumulated by Professor Whitney,t strongly 
sustain the inference based on the history of organic life, 
(c) Cause of Secular Deterioration of Climates. — This 
conclusion being admitted, the most probable explanation 
might seem to be the progressive cooling of the earth. 
This is the explanation generally offered by geologists. 
There must, assuredly, have been an age when the surface 
temperature of our planet was largely influenced by the 
excessive heat of the interior. It is not easy to doubt 
that this influence must have been experienced to some 
extent, during the earlier periods of organic life. Still, the 
present influence of the interior is practically nil ; and in- 
vestigation shows that a crust of very moderate thickness 
would not transmit sufficient warmth to affect the surface 
to any important extent. "Ten, twenty, thirty times the 
present rate of augmentation downward," says Sir Will- 
iam Thomson,! " could not raise the surface temperature 
of the earth, and air in contact with it, by more than a 
small fraction of a degree Fahrenheit. The earth might 
be a globe of white-hot iron covered with a crust of rock 
2,000 feet, or there might be an ice-cold temperature 
within thirty feet of the surface, yet the climate could 
not, on that account, be sensibly different from what it is, 
or the soil be sensibly more or less genial than it is for the 
roots of trees or smaller plants." § 

♦■Whitney, op. cit., 543-57. t Whitney, op. cit., 121-204. 

X W. Thomson, Trans. Geol. Soc, Glasgou\ v. 250. 

§In connection with this we are reminded of the summer vegetation of 
northern Siberia and sub-arctic America, growing luxuriantly upon a soil under- 
laid, at the depth of a few inches, by a permanent stratum of ice or frozen 
earth. 



GENERAL REFRIGERATION. 487 

M. Rey de Morande, also, has recently recorded the opin- 
ion that " the great uniformity of terrestrial vegetation 
till the Cenomanian epoch, and gradual differentiation 
since, according to latitude, the gradual invasion of south- 
ern regions by trees with deciduous leaves, and disappear- 
ance of all vegetation in polar regions are phenomena " 
not only testifying to changes in terrestrial climates, but 
"explicable only by gradual diminution of solar heat."* 
We are constrained, therefore, to ascribe the lowering 
of terrestrial temperatures to the secular cooling of the 
sun. No other theory has been found free from fatal 
objections. Among the attempts made to explain the 
secular cooling of climates, "the only hypothesis of all 
hitherto suggested that has received no favor from any 
professed geologist, is that of a warmer sun — the one 
hypothesis that is rendered almost infinitely probable by 
independent physical evidence and mathematical calcula- 

tion."t 

We seem, therefore, to face the impressive fact that 
human experience is able to testify to some actual abate- 
ment of the force of the sun, and that the testimonies of 
the rocks under our feet affirm and extend the grand con- 
clusion that the sun's remoter history has been a history of 
cooling, and that, consequently, the future must witness a 
further diminution of solar light and heat. 

(2.) Deductive Consider atioiis Touching Secidar Re- 
frigeration. — The ultimate refrigeration of the sun and 
planets is only another expression for the dissipation of the 
energy of the system. As all the forms of energy in the 
known universe are mutually convertible, so, also, the 

*Nature, xxvii, 119, Nov. 30, 1882, from proceedings of Acad, des Sciences, 
Nov. 20, 1882. 

tSirW. Thomson, Trans. GeoL Soc, Glasgow, v, 250. Compare, also, ic?., 
iii, 16, 17. Mr. S. V. Wood maintains that the earth's "glacial period" was 
caused by a diminution in the heat-emitting powers of the sun.— Geoloff. Mag., 
July, 1882. 



488 PLANETARY DECAY. I 

tendency of the universe is toward the transmutation of 
all other forms of energy into heat. The tendency of 
heat is toward diffusion and equilibrium through the pro- 
cesses of radiation and conduction. In other words, the 
time is foreshadowed when all parts of the solar system 
and of the material universe will have attained a uniform 
thermal condition, and all exchanges of heat w^ill have 
ceased. And this is the finality to be anticipated after all 
other forms of energy shall have been transformed into 
heat. In that eventuality, all the forces of nature will 
have attained an equilibrated or exhausted condition. No 
more motion — no more light or electricity, or heat — the 
last course of physical change will have been complete. 

More than twenty-three years ago I was led to the 
adoption of such views, and recorded them in these words: 
"All the present motions of the universe, whether physical 
or physiological, are but the phenomena attendant upon 
the progression of matter toward a state of ultimate equi- 
librium. * -5^ * The tendency of all physical forces 
toward a state of equilibrium and rest will result in a com- 
plete equilibrated diffusion of all self-repellant matter, and 
a concentration into one mass of all self-attractive matter. 
* * * It is not likely that the material universe is 
infinite, h^ * * When light, heat, electricity and other 
* imponderable agents' (if any) shall have become uni- 
formly distributed throughout matter, and have thus been 
brought to a state of equilibrity, both in themselves and in 
respect to matter, there can not be either sun, star or other 
radiant source of light and heat, or any of the motions 
produced by these agents in the organic and inorganic 
worlds. * * * There mast have been a beginning to 
this series of evolutions."* 



* The Cycles of Matter, or the Permanence of the Earth and the Destiny 0} 
the Race, Michigan Joarnal of Education, viii, 273-8, Aug., 1860. Compare 
Spencer's chap, xvi (published in 1862), on "Equilibration," in First Principles. 



GEN^ERAL REFRIGERATIOISr. 489 

Such deductions, however, had been reached by Pro- 
fessor (now Sir) William Thomson eight years earlier, 
though information of the fact had not reached the pres- 
ent writer.* His conclusions are as follows: (a) "There is 
at present in the material world, a universal tendency to the 
dissipation of mechanical energy, (b) Any restoration 
of mechanical energy without more than an equivalent 
dissipation is impossible in inanimate material processes, 
and is probably never effected by means of organized 
matter, either endowed with vegetable life or subjected to 
the will of an animated creature, (c) Within a finite 
period of time past, the earth must have been, and within 
a finite period of time to come, the earth must again be, 
unfit for the habitation of man as at present constituted, 
unless operations have been, or are to be performed, which 
are impossible under the laws to which the known opera- 
tions going on at present in the material world are sub- 
ject."t 

According to this doctrine, the heat of our system — 
chiefly solar — on which all its activities depend, is under- 
going a gradual dissipation in infinite space. It is not 
annihilated, but it is lost to us. In the distant future, all 
parts of the system will be reduced to the mean tempera- 
ture of space, and the wheels of the organism will cease 
to move. 

We may anticipate that the cooling sun will pass 
through phases similar to those of forming planets. A 
liquid central globe will grow, and, as it enlarges, solidi- 

* Professor W. Thomson's Memoir, On a Universal Tendency to the Dissi- 
pation of Mechanical Energy, was read before the Royal Society of Edinburgh, 
April 19, 1852, and communicated by the autlior to the London, Edinburgh and 
Dublin Philosophical Magazine for publication, October, 1852, Series IV, vol. iv, 
pp. 304-6. 

tSee also the celebrated essay of Helmholtz on tha Interaction of Xa'ural 
Forces, first presented as a lecture at Konigsberg, in 1%^^ — Correlation and Con- 
servation of Forces, Youman's ed., 242-4, etc, Ma3'-er, also, glanced in the 
same direction, in 1851, but he only raised a query. — /c^. 355. 



490 PLANETARY DECAY. 

fication will appear at the core. It will become incrusted. 
Its light will grow ruddy and dim. The vapors of water 
will condense in the sun's atmosphere. A stormy stage 
of long duration will ensue. Surface Avaters will accumu- 
late to some extent upon the darkened exterior. We may 
infer, however, that the relative supply of water will be 
scant. The pores of the fire-formed rocks will eagerly 
drink it up. The cooled and planetary surface will 
emerge from the tumult of the secular storm; but a star- 
lit firmament will overhang it. Its own inherent warmth 
may, for a secular period, preserve a habitable tempera- 
ture; but if organic creatures find existence on it, they 
must possess nocturnal instincts. Later on in the eterni- 
ties, this sunless planet — this exhausted and planetized 
sun — will have felt the chill of surrounding space. In 
the remotest finalit}^ which deductive science can reach, 
the sun and planets will have been gathered in one central 
mass. All fire and light will have been extinguished. 
No relative motion will survive — only the dead, cold 
corse will rotate on an axis and trav^el onward in its mys- 
terious, endless, aimless course through the eternities still 
to come.* 

Thus, by the telescope of deductive science, we are 
able to glance "through the corridors of time" to come, 
and anticipate with assurance the approach of events as 
remote in the coming direction as those primordial events 
in the opposite direction which we have seen connected 
with the cradle of the Solar System. But in so distant a 
glance all perspective is lost. Like the stars in the firma- 
ment, those events are projected upon one common 
ground. It is impossible to assert in what order these 
final consummations will be realized. We only know they 

* The present writer has reflected much on these eventualities. See, besides 
the memoir already cited, Tlie Ladles' Repository, Cincinnati, Nov. and Dec, 
1863, and Jan., 1864; Sketches of Creation, 1S70, 380-431, and various other 
publications. 



GENERAL REFRIGERATIOiq-. 491 

are inclosed in the future. The sun will probably assume 
a planetary condition only after the last precipitations 
shall have taken place. The continents may be levelled 
before the synchronistic stage of the earth and moon is 
reached. The precipitative tendencies of tidal action 
may exceed those resulting from resistances encountered 
in planetary space. Whatever the order of progress to- 
ward these planetary issues, and to whatever distance 
removed, these tendencies are so many categories of 
change which demonstrate that a terrestrial, and more 
generally a planetary, and even a cosmical, finality must 
be reached. The world is finite in duration. The Solar 
System is finite. The entire cosmical organism is finite in 
duration. That which is approaching a limit to its exist- 
ence in one direction has proceeded from finite limits in 
the opposite direction. There was a time when the cos- 
mical organism began to exist. Even if it was an older 
framework reorganized, it was a new beginning. What- 
ever the number of times it had been begun, there was a 
first time. If there was a first time, then at that moment 
cosmical existence was out of the order of causal rela- 
tions in the natural world. If there was not a first 
organization, then the cosmic organism is eternal; it does 
not run doion or wear out; it is out of the order of 
causal relations in the natural icorld. 

3. Hevii^ification of a Dead Universe. — The ultimate 
precipitation upon the sun of all the matter in our system 
would not end the existence of matter or of energy, but 
only the existence of one department of the cosmic 
organism. That other systems have already attained this 
condition can hardly be doubted. Nor is it easier to 
doubt that in the exhaustless and perhaps unexplored 
resources of the cosmic economy some means exist for 



492 PLAKETARY DECAY. 

restoration of an effete system to a renewal of intense 
cosraical activity.* 

Nor would the complete equilibrium of the total energy 
of the visible universe end the existence of matter or of 
energy. We must still believe in an appointed reexcita- 
tion of the slumbering potencies of the cosmic elements. 
By what natural means this could be effected, we cannot 
even surmise. 

A suggestion tov/ard a possible means for this end was 
made b}'- Rankine in 1852, soon after the appearance of 
Thomson's memoir, f He holds that the interstellar me- 
dium must be perfectly transparent and diathermanous, 
and thus "incapable of acquiring any temperature what- 
ever, and all heat ^vhich arrives in the conductible form at 
the limits of the atmosphere of a stsir or planet will there 
be totally converted, partly into ordinary motion by the 
expansion of the atmosphere, and partly into the radiant 
form. The ordinary motion will again be converted into 
radiant heat, so that radiant heat is the ultimate form to 
which all physical energy tends. * * * l^^ \^ j^q^ \^q 
supposed that in all directions round the visible world the 
interstellar medium has bounds, beyond which there is 
empty space. Then, on reaching those bounds, the radi- 
ant heat of the world will be totally reflected, and will 
ultimately be concentrated into foci. At each of these 
foci the intensity of heat may be expected to be such 
that should a star (being at this period an extinct mass of 
inert compounds) in the course of its motions arrive at 
that part of space, it will be vaporized and resolved into 

* Spencer: Fii^st Principles, Am, ed., 480. So Kant: Kann man nicbt glau- 
ben, die Xatur, welche vermogend war, sich aus dem Chaos in eine regelmiissige 
Ordnung und in ein geschicktes Sj'stem zu setzen, sei ebenfalls im Stande aus 
dem neuen Chaos, darin sie die Verminderung ihrer Bewegungen versenkt hat, 
sich wiederum eben so leicht herznstellen, und die erste Verbindung zu emeu- 
em?— Kant, Werke, Harteustein ed., i, 302. 

t W. J, M. Rankine: On the Reconcentration of the Mechanical Energy of 
the Universe, Phil. Mag., IV, iv, 358-60, Nov., 1852. 



GENERAL REFRIGERATION. 493 

elements. * * * These opposite processes may go on 
together. Some of the luminous objects which we see in 
distant regions of space may be not stars, but foci in the 
interstellar ether." 

The improbability of this curious conception impresses 
itself at once. The limitation of the ethereal vehicle of 
starry radiations is not easy to grant, though thinkable. 
The luminiferous medium is not perfectly transparent and 
diathermanous. The mode of action by which the radia- 
tions are returned is too mysterious to make part of a 
hypothesis. The concentration of the rays is equally mys- 
terious. The existence of moving bodies is incompatible 
with the premise of a full equilibrium of cosmic forces. 
And finally, if all these doubts could be removed, the 
intense focal heat contemplated would be an impossibility. 

The last point has been fully demonstrated by Clau- 
sius.* He proves that it contravenes the second law of 
thermodynamics, which declares that " it is impossible by 
the unaided action of natural processes, to transform any 
part of the heat of a body into mechanical work, except 
by allowing heat to pass from that body into one of a 
lower temperature." f Clausius has simplified the expres- 
sion of this law in a way which suits the present case, by 
stating it thus: '■'■Heat cannot pass of itself , i. e., icithout 
compensation, from a colder to a loariner hodyy Now 
the conception of Rankine requires that radiations of 
energy shall be concentrated through reflection, in such a 
way that a body placed at a focal point shall become 
heated to a higher temperature than the bodies possess 
from which the radiations proceeded. Clausius, on the 

*R. Clausius: Ueber die Concentration von Wdrmeund Lichlstrahlen und 
die Grdnzen ihrer Wirkung, Pogg. Annal., cxxi, 1-44, 1864, read at the Zurich 
Natural History Society, June 22, 1863 ; more fully elaborated in Die Mechan- 
ischeWdrmetheorie, 2d ed., i, 815-53. 

t Maxwell: Theory of Heat, \b'?>\ Clausius: Die Mechanische Wdrtnetheorie . 
i, 72, 81, 82. 



494 PLAIs"ETARY DECAY. 

contrary, proves (1) " That the force of emission of a body- 
depends not alone on its constitution, but also on the na- 
ture of the surrounding medium, in such a way that the 
force of emission in different media is inversely as the 
square of the velocity of propagation of the rays in the 
medium, or directly as the square of the coeJBficient of 
refraction of the medium," and (2) "That the second law of 
thermodynamics is valid not only in cases where no con- 
centration takes place, but equally in cases where it takes 
place." It follows that no such method of reconcentration 
of cosmical energy as Rankine suggested is compatible 
with the established processes of nature. Nor is science 
able, at present, to point out any natural means by which 
the dissipation of energy from our system may be arrested, 
or the impending equilibrium of energy throughout the 
universe, again disturbed. 

Nevertheless, there remains to us an abiding convic- 
tion, as expressed by Kant in the middle of the last cen- 
tury, and which Mr. Spencer bases on a priori grounds, 
that the activities of a dead universe may be renewed. 
" Motion," he says, " as well as matter, being fixed in 
quantity, it would seem that the change in the distribu- 
tion of Matter which Motion effects, coming to a limit in 
whichever direction it is carried, the indestructible Mo- 
tion thereupon necessitates a reverse distribution. Ap- 
parently, the universally coexistent forces of attraction 
and repulsion, which, as we have seen, necessitate rhythm 
in all minor changes throughout the Universe, also neces- 
sitate rhythm in the totality of its changes^' — produce now 
an immeasurable period during which the attractive forces 
predominating cause universal concentration, and then an 
immeasurable period, during which the repulsive forces 
predominating cause universal diffusion — alternate eras 
of Evolution and Dissolution." * These recurrences of 

* Spencer : First Principles^ 48:2. 



GENERAL REFRIGERATION. 495 

cosmical activity and rest were traced in my essay of 1860, 
and designated " The Cycles of Matter." 

The reorganization of a Universe in which the series 
of events has reached the last term attainable by action 
according to known laws, presents before us a problem of 
the same order as that of the origination of matter and 
energy. It may not be necessary to despair of the dis- 
covery of the natural means of recuperation of worn-out 
systems; but, as long as the means remain undiscovered, 
it is philosophically legitimate to contemplate a restitution 
by the intervention of such power as was exercised in the 
first institution of cosmical order, and in the origination of 
the matter, the efficiency and the method revealed in the 
living cosmos. 



CHAPTER T. 

HABITABILITY OF OTHER WORLDS. 



Da wir durch die spectralaualyse wissen, dass die cheniischeu Elemente, 
aus deu Planeten imd Fixsterne bestehen, nicht toto genere von den auf der 
Erde anzutreffenden verscliieden sind, sowerden wir auch beziiglich der organ- 
ischen Entwickelungen auf den Planeten alinliche Wirkung schliessen durfen. 

— ZOLLNEK. 

Toutes les verites mathematiques doiveut etre les menies dans Tetoile Sirius 
et dans notre petite loge.— Voltaire. 

L'homme fait pour la temperature dont il jouit sur la terre, ne pourrait pas, 
selon toute apparence, vivre sur les autres planetes; mais ne doitil pas y avoir 
une infinite d' organisations relatives aux diverses temperatures des globes de 
cet univers ?— Laplace. 

If the reader should have a mind to amuse himself with probable guesses 
about the furniture of the planets of our solar system, what countries 'tis prob- 
able are there, what vegetables are produced, what minerals and metals are 
afforded, what animals live there, what parts, faculties and endowments they 
have, with much more to the same purpose, he may find a pleasant entertain- 
ment in the great Mr. Christian Huygens' Cosmotheoros, and some other authors 
that have written on the subject.— William Dekham. 1714. 

§1. SOME REFEREXCES TO LITERATURE ON THE 
SUBJECT. 

THE habitabilit}^ of other worlds is a question on which 
a vast amount of speculation has been expended. It 
has been the general belief that many other worlds are 
inhabited.* Dr. Lardner argued the habitability of the 

* Giordano Bruno: Be Vlajinito Universo e Mot\di J/mumerabili, 1584; 
Christian Huygens : Cosmotheoros, sive de Terris Calestibus, earumque ornatu 
conjecturce, Huygenii Opera, tom. ii, 645-722, Eng. translation, Tlie Celestial 
Worlds Discovered, or Conjectures concerning the Inhabitants, Platits and Pro- 
ductions of the Worlds in the Planets, 1698, 2d ed. 1722 ; William Derham : Astro- 
theology, 1714, 3d ed. 1717, pp. xlvii, liii, liv, 9th ed. 1750, pp. xxx, xxxiv, xxsv : 
Immanuel Kant: Allgenieine Naturgeschichte, etc., 1755, 3ter. Theil, Sammt- 
liche Werke, i, 329-45 ; Laplace: Systlme du Monde, 5th ed., 1824. 389; Fonte- 
nelle: Dialogues on the Plurality of Worlds, 1686, 2d ed. 1719; Sir David Brew- 
ster: More Worlds than One; C. Flammarion: LaPluralite des Mondes ffabites, 

496 



HUMAN STA]^DARD Js^OT ABSOLUTE. 497 

moon and all the planets.* Dr. Brewster held similar 
views. Some have even maintained that the physical con- 
dition of the body of the sun may be such as to produce a 
state of habitability. f Sir William Herschel is said to 
have conjectured that the solar spots are the highest points 
— some 600 miles high — of a cool and habitable globe. J; 
On the contrary, the habitability of other worlds has 
been denied on theological grounds. § It was formerly a 
common theological belief that the biblical teaching is in- 
compatible with the doctrine of other worlds of beings. 
Dr. Whewell disputed the plurality of worlds by appeal to 
scientific evidence. || 

§2. THE HUMAN STANDARD OF HABITABILITY NOT 
ABSOLUTE. 

The question of the habitability of other worlds has^ 
generally been discussed from the assumption that all other 
corporeal beings must be clothed in flesh and bones sim- 
ilar to those of terrestrial animals, and must be adapted to 
a similar physical environment. But it is manifest, on a 
moment's consideration, that corporeality may exist under 
very divergent conditions. It is not at all improbable that 
substances of a refractory nature might be so mixed with 
other substances, known or unknown to us, as to be capable 

8vo., 1864; R. A. Proctor: Other Worlds than Ours ; C. DuPrel: Die Planeten- 
bewohner und die Nebularhypothese, Neue Studien zur Entiviclcelungsgeschichte 
des Weltalls, gr. 8°, Leipzig, 1880; Bentley: Soyle Lectures, Lect. viii, ed. 1724, 
p. 298, seq. ; W. Miller: The Heavenly Bodies, their Nature and Habitability, 344 
pp., London, 1883. 

* Lardner : Museum of Science and Art. « 

t President Forbes: Reflections on the Sources of Incredulity ivith regard to 
Religion, Edinb. 1750, p. 3; Dr. Elliot, Edinb. Encyc. , Art. Astronomy, vol. ii, 
616; Gentlemen's Magazine, 1787, 6:36. Compare also the works of Flammarion, 
Jean Reynaiid, Babinct and Pioger. 

il have not yet found this opinion recorded in his writings. 

§ Maxwell: Plurality of Worlds, 182X He holds that the Newtonian phil- 
osophy contains principles " which lie at the foundation of all atheistical sys- 
tems." 

II Whewell: Of the Plurality of Worlds. 
32 



498 HABITABILITY OF OTHER WORLDS. 

of enduring vastly greater vicissitudes of heat and cold 
than is possible with terrestrial organisms.* The tissues of 
terrestrial animals are simply suited to terrestrial condi- 
tions. Yet even here we find different types and species 
of animals adapted to the trials of extremely dissimilar 
situations. 

Nor is it to be supposed that the plans of structure of 
animals on other habitable planets bear necessarily any 
analogy to organic plans on the earth. That an animal 
should be a quadruped or a biped is something not depend- 
ing on the necessities of organization, or instinct, or in- 
telligence. That an animal should possess just five senses 
is not a necessity of percipient existence. There may be 
animals on the earth which neither smell nor taste. There 
maybe beings on other worlds, and even on this, who pos- 
sess more numerous senses than we. The possibility of 
this is apparent when we consider the high probability that 
other properties and other modes of existence lie among 
the resources of the cosmos, and even of terrestrial matter. 

There are animals which subsist where rational man 
would perish — in the soil, in the river and the sea. No 
reason can be assigned why aquatic respiration should be 
confined to brute animals. On a planet without land, like 
Uranus, high intelligence might be enframed in a gill- 
bearing embodiment; and resources and stimuli for intel- 
lectual activity might be discovered in the bottom of the 
ocean, or in the infinitesimal world which fills a slimy pool, 
or "swarms upon the thickly peopled air.'' Nor is incor- 
porated rational existence conditioned on warm blood, nor 
on any temperature which does not change the forms of 
matter of which the organism may be composed. There 
may be intelligences corporealized after some concept not 

* While these pages are in the printer's hands, similar suggestions appear 
from others. See Charles Morris, Amer. Naturalist, xvii, 930-1, Sept., 1883, and 
E. D. Cope, Science, ii, 279, Aug. 31, 1883, in an address at Minneapolis. 



HUMAN" STANDARD N-QT ABSOLUTE. 499 

involving the processes of injestion, assimilation and re- 
production. Such bodies would not require daily food and 
warmth. They might be lost in the abysses of the ocean, 
or laid up on a stormy cliff through the tempests of an 
arctic winter, or plunged in a volcano for a hundred years, 
and yet retain consciousness and thought. It is conceiv- 
able. Wh)^ might not psychic natures be enshrined in in- 
destructible flint and platinum? These substances are no 
further from the nature of intelligence than carbon, hydro- 
gen, oxygen and lime. But, not to carry the thought to 
such an extreme, might not high intelligence be embodied 
in frames as indifferent to external conditions as the sage 
of the western plains or the lichens of Labrador — the 
rotifers which remain dried for years or the bacteria which 
pass living through boiling water. Again, there is no 
reason why a given amount of light should accompany 
intelligent organization. Many animals, not among the 
least intelligent, find the night their appropriate period of 
activity. Some exist and thrive in rayless caverns and 
ocean depths. On a planet dimly lighted, like Neptune, 
men might be organized with pupils as large as silver dol- 
lars, or even as large as dinner plates. Vision might be as 
distinct on Neptune as on the earth. As to warmth, a 
blanket of vapors may keep it in and accumulate it to the 
requisite extent. And in that distant time when the sun 
shall become planetary, large-orbed men may move about 
in star light over a surface sufficiently warmed by internal 
heat, and forms of vegetation may flourish, and supply 
food for man and beast without the stimulus of solar radia- 
tions. These suggestions are made simply to remind the 
reader how little can be argued respecting the necessary 
conditions of intelligent, organized existence, from the 
standard of corporeal existence found upon the earth. 
Intelligence is, from its nature, as universal and as uniform 
as the laws of the universe. Bodies are merely the local 



500 HABITABILITY OF OTHER WORLDS. 

fitting of intelligence to particular modifications of univer- 
sal matter and force. 

§3. HABITABILITY UNDER THE HUMA?s^ STANDARD. 

But let us consider how far other worlds are suited for 
habitations for beings akiu to ourselves. This is a question 
for scientific consideration. The answer to the question, 
when asked with reference to each of our planets, is to 
be sought in what has been already said concerning the 
physical conditions of the planets. Mercury is not habit- 
able for beings like ourselves. Proximity to the sun 
results in a destructive degree of heat, if it does not 
actually prevent all water from finding a resting place on 
the planet's surface. The sun's apparent diameter from 
Mercury is more than two and a half times as great as 
from the earth. 

In reference to Venus, and possibly also Mercury, we 
must bear in mind that the relations of heat and water 
are such that water might exist as a dense and permanent 
envelope of clouds. This seems the more probable, even 
for Mercury, in view of Professor Langley's determination 
of the astonishing rate of radiation in a thin atmosphere. 
At the upper limit of an atmosphere sufficiently dense to 
support aqueous vapor, it seems not irrational to assume 
that escape of heat would be rapid enough to condense 
water even in the fierce solar heat experienced at Mercury's 
distance from the sun. So far as the existence of a 
stratum of clouds is possible, this would, of course, serve 
as a screen for the surface of the planet, so that compara- 
tively little of the sun's direct radiation would interfere 
with habitability. In this view there seems no great im- 
probability that both these planets are inhabited by intel- 
ligences organized somewhat like ourselves. The amount 
of water belonging to these planets being in less propor- 
tion than on the earth, the processes of evaporation and 



HABITABILITY UNDER THE HUMxVN STANDARD. 501 

precipitation must keep it in active circulation. No very 
considerable bodies of water can be supposed to exist, 
and a large proportion of the entire surface must be ac- 
cessible to occupation and cultivation. The final absorp- 
tion of the water will, therefore, occur at a relatively 
early epoch, when, of course, habitability must end. 

Thus, the first thought of these sister worlds suggests 
that they may be the homes of beings kindred to our- 
selves. Then the knowledge of the intensity of the solar 
radiations on their surfaces seems to preclude the belief in 
their habitability. But finally, a discovery of natural 
means for the alleviation of excessive heat leaves us with 
the conviction that after all we may have neighbors on 
the contiguous planetary territory. As to their organiza- 
tion, while it is profoundly true that under circumstances 
extremely diverse from those under which we live, ex- 
tremely diverse organizations must be conceived both 
possible and probable; yet where the divergence is no 
greater than on the interior planets, all the fundamental 
functions and processes may be conceived analogous to 
our own. There is so widespread uniformity in the nature 
and action of physical forces that we may suspect the 
same in regard to organic structures and activities. As 
organization in its forms and functions is conditioned by 
the properties of matter and the laws of energy, and 
these conditions are widely pervasive throughout our sys- 
tem, we have good ground for believing that plans of 
organization and modes of activity are fundamentally 
analogous under all planetary conditions not more diverse 
than we conceive those of the earth and the interior plan- 
ets to be. In fact, there exist contrasts of condition upon 
the earth nearly as wide as the contrasts between the 
earth and Venus. In all these contrasted situations 
nature employs the same fundamental plans of organ- 
ization and functioning. 



502 HABITABILITY OF OTHER WORLDS. 

On the whole, as intelligence must be revealed in the 
cosmic organization of Mercury and Venus, there are pre- 
sumably intelligent beings in correlation with the intelligi- 
ble world; and as the conditions of corporeality are so far 
analogous to those on the earth, we may reasonably con- 
ceive organic intelligences on those planets who have 
power of locomotion by muscles and bones; who eat and 
respire; who suffer and enjoy; who cognize light and heat 
and sound; who observe and reflect, imagine and aspire; 
and, while ignorant, probably, of many or most of our 
arts, have invented many others of which we never 
dreamed, and achieve accomplishments which would be 
miracles to us. 

The moon, in the absence of air and water, must be 
without inhabitants akin to ourselves. Though the moon 
has passed through the successive phases of a cooling 
globe, I cannot think the violence which must have 
reigned on its surface before synchronistic times would 
have permitted the existence of an organic being. Nor, 
since the synchronistic period began, have the conditions, 
as far as we can judge, been endurable. The fortnightly 
alternations of extreme heat and extreme cold must prove 
fatal to all organic life with which we are acquainted. It 
is pleasant to think of kindred beings on a neighboring 
world, though we might not by any possibility open inter- 
course with them. It is pleasant even to believe that the 
moon may have been inhabited in a former planetary 
period. It creates a sense of relation to distant parts of 
the universe to believe that other beings.. may even have 
lived there and passed away. To know that the lunar 
surface is a wild scene of desolation, and to know that 
only the unconscious forces of inorganic nature have ever 
interrupted the oppressive silence of the planetary soli- 
tude, seems to sunder a bond of sympathy with the uni- 
verse, and isolate mankind on an island rock where no 



HABITABILITY UNDER THE HUMAN STANDARD. 503 

message can ever arrive. But it is better to know the 
truth than to indulge in fancy. The moon is probably no 
more uninhabitable in the present period than it has been 
during its entire history.* 

Mars, according to the scientific indications, presents 
conditions more nearly approximating the demands of 
habitability than any other planet besides the earth. It 
seems almost certain, however, that the meridian of its hab- 
itable phase is passed. The sun's apparent diameter from 
Mars is two-thirds his size seen from the earth, and his 
light and heat are only three-eighths as much as the earth 
receives. As the intensity of gravity on the surface of 
Mars is only three-eighths the intensity of gravity on the 
earth, many diverse conditions would be introduced. A 
man of ordinary agility would be able to leap over a wall 
twelve feet hi^h. If on the earth, a strong man is able to 
support 26 pounds in his palm at arm's length, and his 
arm is equivalent to four pounds in his palm, he might be 
42J feet high before the weight of his arm would become too 
great for him to extend it; but on the planet Mars, such 
a man might be 109 feet in height. f Again, considering 

* In my brochure, entitled Geology of the Stars, speaking of the compara- 
tively rapid succession of lunar periods, I said: "The zoic age of the moon 
was reached while yet our world remained, perhaps, in a glowing condition. Its 
human period was passing while the Eozoon was solitary occupant of our 
primeval ocean." Mr. Fisk, in his Cosmic Philosophy (i, 400, note), has cited 
this as '-an example of the too hasty kind of inference which is often drawn in 
discussing the question of life upon other planets." Mr. Fisk misapprehends, 
for it is not stated that human beings ever lived, or could have lived, upon the 
moon. The allusion is simply to that stage of lunar evolution which corre- 
sponded to the human stage in terrestrial evolution. 

+ If IV — the total weight a strong man's arm can support, including weight 
of arm and load, and p — weight of arm, and n equal number of times greater, 

w 
in any dimension, the arm is which could bear no load, then n — - (Young's 

Mechanics, Williams' ed., p. 113), and if g' = gravity on any planet compared 
with gravity on the earth, then, on that planet 

Now, if we assume that a man can raise 26 pounds at arm's length, and that 
his arm is equal to 4 pounds in his palm, then n = 7.5; and if a strong man's 



504 HABITABILITY OF OTHER WORLDS. 

that the Martial atmosphere is likely to be .105 that of the 
earth, and is spread over .2828 the same amount of sur- 
face its density on the surface of the planet is only .1379 
that of the earth's surface atmosphere, giving a pressure 
on the mercurial barometer of about 4.1-1 inches. The 
height of the Martial atmosphere reduced to uniform sur- 
face density would be 2.694 times that of the earth's 
atmosphere, or about 13.56 miles. The surface density of 
the Martial atmosphere is only such as would be attained 
on the earth at the height of 10.2 miles.* This implies a 
universal state of atmospheric tenuity on the surface of 
Mars which has not been found compatible with any ter- 
restrial life. The simple difference in mass creates condi- 
tions which would render the surface of Mars completely 
untenable by any human being; and this consideration, it 
might have been stated, applies as well to Mercury and 
the Moon. But this is no proof that organic beings 
suited to such atmospheric pressure do not exist. Ani- 
mals are dredged from oceanic depths where the pressure 
as much exceeds the sea level pressure as the atmospheric 
density of Mars falls below the terrestrial standard. Ani- 
mals are adapted as they are because the conditions are 
as they are; and we may feel assured that if the condi- 
tions were different, organic adaptations would be differ- 
ent correspondingly. The conceivable range of adapta- 

height is 68 inches, the height of a man on the earth who could barely extend 
his arm — since his height is proportional to his arm's length — would be 68 
inches X 7.5 — 42.5 feet; and the height of such a man on Mars would be 

^ == 108.95 feet. 

*U h — the height at which the density of the earth's atmosphere is - that 

at sea level, then, since the density diminishes in a geometrical ratio as the 
height increases in an arithmetical ratio, the height 2 A will give a density of 

— ; the height 3 A will give a density of —'and generally the height xh will 

give a density of — • But — = .1379. whence, if w, = 2 and h = 2.705 miles, x 

= 3.77 and xh = 3.77 X 2.705 = 10.2 miles. 



HABITABILITY UNDER THE HUMAN^ STAKDARD. 505 

tions is limited only by the physical properties of inorganic 
matter. 

On the planet Jupiter, the mass so much exceeds that 
of the earth that all the relative conditions are reversed. 
I have shown that atmospheric density is nearly 6^ times 
as great as on the earth. Hence respiration would only 
need to be G^ times less active. On the contrary, the force 
required to sustain the body against gravity would be more 
than 2-J- times as great, and all weights would be 2^ times 
as difficult to move. This increased weight of the body 
and limbs would render comparatively less efficient similar 
muscular efforts, while the gravitational resistances to be 
overcome would be greater. A man 16^ feet high would 
be barely able to extend his arm at a right angle with his 
body. If ever the planet Jupiter attains a habitable con- 
dition its organic beings will be limited in some such man- 
ner as these numerical results imply. 

The apparent diameter of the sun from Jupiter is only 
.2392 or ^-^-^ the same from the earth; and the sun's radiant 
energies in the forms of light, heat, actinism and attrac- 
tion, are only -^-j of the same at the earth. Were the 
sun's heat reduced on the earth to ^L. its present amount, 
it is manifest that all organic life must perish. If ever, 
therefore, the inherent temperature of Jupiter subsides so 
far as to bring his surface condition to that of the earth, 
no Jovian climate will be such as animal organization can 
endure. As his actual surface temperature, however, will 
always be compounded of the effects of solar radiation 
and of conduction from within, there will be an epoch 
when his actual mean surface temperature will be the 
same as the earth's actual mean surface temperature. The 
vicissitudes of the seasons will be -^tj as great as on the 
earth — regardless of the effect of less obliquity of the 
axis — and the diurnal and nocturnal fluctuations of tem- 
perature will be only ^ as great. Owing to a denser at- 



506 HABITABILITY OF OTHER WORLDS. 

mosphere, the fluctuations will be even less than this. 
The higher inherent temperature of the soil will result in 
so much radiation from the planet that on a planet with 
so large a supply of water, and in an atmosphere so dense 
as Jupiter's the sun's deficient heat may be largely com- 
pensated by suppressed radiation from the planet. The 
situation will be that of a mild and dimly lighted "stove" 
in horticultural operations, highly suitable for the growth 
of mushrooms. It will be perpetual evening. It can not 
be doubted that corporeal intelligences might be coordi- 
nated to such a physical condition. For the present, how- 
ever, we have not the slightest grounds for imagining the 
existence of organic populations upon the surface of 
Jupiter, unless they depart in some very extreme way 
from the terrestrial standard. 

As to the planets remoter from the sun, I have oifered 
reasons for considering them advanced to a state of total 
refrigeration. They cannot therefore, be conceived as 
habitable. There was a time, however, in the history of 
each, when its stage of cooling produced a surface tem- 
perature suited for organic life. At that stage, the re- 
lations of organic beings on their surfaces were similar to 
those which may be anticipated for Jupiter, with all the 
greater divergences from the terrestrial condition which 
depend on distance from the sun carried to successively 
greater extremes, and successively larger proportions of 
water and gaseous substances. On Neptune the apparent 
diameter of the sun is but -^-^ the sun's apparent diame- 
ter to us, and his heat and light are reduced to -g-i-Q- the 
heat and light received by the earth. This light would, 
nevertheless, be equal to about 69 of our moons. The 
excess of water however, on all the distant planets, in ac- 
cordance with views heretofore presented, would probably 
render them, in all stages of existence, totally uninhabit- 
able for beings like ourselves. But it is always to be re- 



HABITABILITY UNDER THE HUMAN STANDARD. 507 

membered that other beings suited to the actual exigences 
of the environment, may have occupied the situation. 

The earth, then, so far as we can reason, is in the middle 
of the habitable zone of the solar system, if our own na- 
tures are assumed as the criterion of habitability. On 
either side, the rigor of the physical conditions seems to 
proclaim our system a voiceless and lifeless desert. Even 
our near neighbor, the moon, lies on the borders of 
this desert. Within the vast limits of the solar system 
there is but one happy niche where corporeal organization 
according to our standard can enter into material relations 
with the physical environment. The conclusion is un- 
doubtedly disappointing. But the impression is further 
deepened by the reflection that on our own congenial 
planet life is hemmed in between the terrestrial surface 
and the upper limit of a film of atmosphere not thicker 
than the mean depth of the film of ocean which enwraps 
the solid globe. The entire human family swarms within 
a sheet of atmosphere not over three miles thick. Above, 
are the rigors of unendurable cold, and the horrors of un- 
supported respiration. Below, are the impenetrable rocks 
or the submerging waves or the internal fires. Even the 
space about us and nearest to us is, for the greater part, 
inaccessible to man, and unvisited by any organic being. 
We need not wonder that corporeal existence is a rarity 
through all the realm of our system. 

But there are other suns and other planetary systems, 
and other worlds which possess the conditions of habita- 
bility. When we look on the hosts of stars, and consider 
that if only one habitable planet wanders about each sun, 
we understand that the number of habitable worlds is 
countless. In this view, space seems to be densely popu- 
lated. We have neighbors ; they live beyond impas- 
sable barriers, but they gaze on the same galaxy, and 
we know they are endowed with certain faculties which 



508 HABITABILITY OF OTHER WORLDS. 

establish a community between them and us. How- 
ever conformed bodily, whatever their modes and means 
of organic activity, we know that they reason as we 
reason, and interpret the universe on the same princi- 
ples of logic and mathematics as ourselves. The or- 
bits which their planetary homes describe are ellipses ; 
they have studied the same celestial geometry as our- 
selves ; they have written their treatises on celestial 
mechanics ; they have felt the impact of the luminous 
wave of ether ; they have speculated on the nature of 
matter and energy ; they have interpreted the order of 
the cosmical mechanism as the expression of thought and 
purpose ; they have placed themselves in communion with 
the Supreme Thinker, who is so near to all of us that 
his voice is audible alike to the ear of reason in all the 
worlds. 



PART HI. 
GENERAL COSMOGONY. 



Das All einem jener siidlichen Baiime gleicht an denen zu denselben Zeit, 
hier eine Bliithe aufgeht, dort einc Frucht von Zweige fallt.— Strauss. 

Auf gleiche Weise verlassen ganze Welten und Systeme den Schauplatz, 
nachdem sie ihre Rolle ausgespielt haben. * * * Indessen, dass die Natur 
mit veranderlichen Auf tritten die Ewigkeit ansziert, bleibt Gott in einer unauf- 
horlichen Schopfung geschaftig, den Zeug zur Bildung nocli grosserer Welten 
zu formen.— Kant. 

Mit welcher Art der Ehrfurcht muss nicht die Seele sogar ihr eigen Wesen 
ansehen, wenn sie betrachtet, dass sie noch alle diese Veranderungen iiberlebeu 
soil.— Kant. 



CHAPTEE I. 

FIXED STARS AND NEBULAE. 
§ 1. CONDITIONS OF THE FIXED STARS. 

1. Double^ Triple and Multiple Stars. 

THAT some of the fixed stars are the result of the 
gradual condeDsation of nebulous matter about a 
centre was the conjecture of Sir William Herschel. I be- 
lieve that the stars in general have resulted from nebular 
condensation; but in many cases — probably not in all — 
a rotation has arisen whose influence has been perma- 
manently impressed on the course of events. The con- 
dition of our own system, and the history deduced from 
it, make known a natural and probable mode of evolution 
of other systems; and it cannot reasonably be denied 
that many other systems have come into existence in 
a similar way. Other planets, consequently, revolve in 
nearly circular orbits about many other suns. It is not 
impossible, however, that a non-rotating sun should be 
attended by planets which have not been disengaged from 
its own mass. It is, indeed, probable, that many small 
cosmical bodies should have been thrown by contending 
attractions into paths which pass near great centres of 
attraction. While many of these must have moved with 
velocities which would carry them on in hyperbolic curves, 
others may have moved with velocities so low as to pass 
into elliptic orbits, and thus become planets or satellites 
to greater bodies. The comets of our own system seem 
to realize both these conjectures. But a planetary rela- 
tion established in this manner would present an orbit of 

511 



512 FIXED STAES AKD XEBUL.E. 

high eccentricity. Moreover, it seems probable, consider- 
ing the immensity of the intervals of space, and the great 
distance from which a smaller mass would approach a 
greater, that in nearly all cases a velocity would be ac- 
quired too great for the assumption of elliptic orbits. This 
would be especially the case with approaching bodies 
having sufficient mass to constitute a planet. More insig- 
nificant collections of matter would be more under the con- 
trol of central masses. Hence foreign bodies introduced 
into a system would be more probably of a cometary than 
of a planetary character. 

That other suns are attended by planets is a fact of 
observation; though no planetary attendant would be visi- 
ble except such as retain still an incandescent character. 
Hundreds and even thousands of stars have been pro- 
nounced "double;" and, in a number of cases, the two 
components have been observed in a process of revolution 
about the common centre of gravity.* Not less than 
fifteen of these have been observed sufficiently long to 
determine their periods of revolution; and several have 
been actually traced through complete revolutions.! 

It needs hardly be said that no attendant of a sun 
would be visible unless itself of very great magnitude, and 
hence having sufficient mass to compel a visible amount 
of motion in its nominal central body. How many smaller, 
and therefore, invisible, planets though still luminous, 
and how many smaller and darkened planets, may revolve 
about the same centre, is matter open to conjecture; but 

* Struve, in Mensitrce Micrometricce, Dorpat, 1837, enumerated 3,000 double 
stars, most of which had been noted by Sir William Herschel. To this number 
Otto Struve of Pulkova has added 500; and Mr. S. W. Burnham announces that 
he has detected 900 new pairs. Others have reported perhaps 50 new discoveries. 
This makes an aggregate of 4.450 double stars. 

tZeta, of Hercules, has a period of 36 years; Eta, of the Northern Crown, 
a period of 43 years; Zeta. of the Crab, 59 years; Xi, of the Great Bear, 63 
years. Others have still longer periods — one in Virgo being 513 years, and that 
of Gamma, of the Lion, 1,200 years, 



COXDITIOi«"S OF THE FIXED STARS. 513 

I believe we may fairly assume that such planetary attend- 
ants must be exceedingly numerous. It seems a natural 
conjecture that all these luminous attendants of other 
stars are planetary or derived bodies in the same condi- 
tion as once characterized the earth, and more recently, 
perhaps, the largest planet of our system. "These 
planets," says Secchi, "differ from ours only in a single 
point, they are still incandescent, and consequently self- 
luminous." 

What is more remarkable and interesting is the fact 
that many stars appear triple and multiple. Mr. S. W. 
Burnham publishes a list of 53 stars enumerated in Struve's 
catalogue, in which a " closer component " has been more 
recently discovered — the majority of them by himself.* 
These are then so many cases of stars associated in groups 
as high as triplets. But among them are instances in 
which a fourth, fifth, sixth and seventh component has 
been detected. Theta of Orion is a celebrated septuple 
star. The first inference which one feels tempted to draw 
from the phenomena of triple and multiple stars is the ex- 
istence in one system, of more than one planet retaining a 
self-luminous condition. Tt might be suggested, however, 
that even satellites of still luminous planets may retain 
the luminous condition. In this case we should ultimately 
detect orbital motion around one of the components, 
together with motion around the common centre of 
gravity of the system. This is an interesting inquiry for 
astronomy, f 

2. Teynporary Stars. — From time to time during cen- 
turies past, stars have been seen to burst forth into lumi- 
nosity in situations before unoccupied, increase in bril- 

*S. W. Burnham, Science, ii, .35, January 22, 1881. 

+ It is quite possible that two stars under the combined influence of mutual 
attraction and antecedent motion, not approaching sufficiently near for coales- 
cence, should enter upon orbital revolutions about their common centre of 
gravity. 

33 



514 FIXED STARS AXD XEB UL^. 

liancy for a few weeks or months, and then gradually wane, 
changing from white to yellow and red, and finally disap- 
pearing. According to Humboldt, twenty-one such stars 
were recorded during the interval of 2,000 years between 
134 B.C. and 1848 A.D. The most remarkable of these 
occured in 1572 in Cassiopoeia, and was specially studied 
by Tycho Brahe. It exceeded in brillianc}^ both Sirius and 
Jupiter. Another remarkable occurrence took j^lace in 
1604, in Ophiucus, and was studied b}^ Kepler. This star 
nearly equalled Venus in brightness, but at the end of 
fifteen months was so diminished as to be merely a tele- 
scopic object. Another was discovered by Hind, in 1848. 
The one which occurred in Ma}^, 1866, in the Northern 
Crown, exceeded the second magnitude in brightness. 

The last mentioned was spectroscopically investigated. 
According to Huggins, tlie spectrum indicated two dis- 
tinct sources of light, each producing a separate spectrum. 
One was a continuous spectrum crossed by dark lines, 
similar to that yielded by the sun and most of the stars. 
The other consisted of four brilliantly bright lines. The 
first spectrum showed a photosphere of incandescent mat- 
ter either solid or liquid, surrounded by an atmosphere of 
cooler vapors giving rise by absorption to the dark lines. 
The other spectrum showed the presence of an intensely 
luminous gas which, according to Huggins, was appar- 
ently hydrogen at a higher temperature than existed in 
the photosphere of the star. These spectral phenomena 
have prompted the suggestion by Huggins, and separately 
by Rayet and Wolf, that the sudden brightness of the star 
was caused by an outburst of intensely heated hydrogen 
gas, which, by gradual exhaustion, occasioned the waning 
brilliancy of the star. Others have attributed it to colli- 
sion with some other orb; but this idea is set aside b}^ the 
rapidity of the decrease in brilliancy, as well as by the 
supposed periodicity of some temporary stars. 



CONDITION'S OF THE FIXED STARS. 515 

It is now maintained that none of the temporary stars 
are new originations, and that none of them have disap- 
peared from existence, if even from visibility. That 
occurring in the Northern Crown is still tclescopically 
visible; and it is maintained that the new stars of Tycho 
and Kepler may still be seen. In fact, the belief exists 
that the same stars had previously blazed forth more, than 
once — that of Tycho in 945 and 1264, and that of Kepler 
in 393, 798 and 1203. In this view, temporary stars are 
only variable stars with very long periods. But this 
theory needs to be confirmed. 

I think these phenomena can better be coordinated 
with the general tenor of change resulting from the 
genetic development of cosmical bodies. As every cos- 
mical body is, in one stage of its history, thermally lumi- 
nous, and at another, dark, there must be an era in the 
lifetime of each dark body, when it is passing from the 
condition of a luminous to that of a darkened body. 
There must be many stars at present in this transitional 
stage. There must be many more which have served as 
centres of planetary motion, but have since cooled to a 
state of darkened invisibility. There is no reason to 
assume that most stars are luminous. It is probable that 
space is strewn with planetized suns as well as planets and 
satellites. There are as many stages of evolution beyond 
the luminous stage as there are characteristic of it. There 
must be many dead moons lying unburied in the broad 
fields of space. Indeed we may conceive immensity like the 
soil on which human races tread, to be more densely popu- 
lated by the dead than by the living. We dwell in a cos- 
mic cemetery, and the ashes of worlds once quick with 
life strew the pathways of the burning and shining 
lights. 

There are three ways, under this conception of things, 
for explaining the phenomena of a temporary star — or 



516 FIXED STARS AXD XEBUL.E. 

one which bursts forth into visibility and brilliancy in a 
new place, and after a time disappears: 

(1.) Collision of a precipitated planet. I have stated 
that all our planets must be tending toward precipitation 
on our sun. It ma}^ be that after our sun is cooled and 
darkened, some planet will yet remain to be reunited with 
its ancient mother. The reunion will not result from the 
direct fall of the planet toward the sun, but from a spiral 
descent. With ever-increasing velocity the planet will 
approach the central body, and w^ill finally touch it. If 
both bodies are solidified, a degree of friction will be 
developed almost exceeding computation. If revolving 
wheels sometimes ignite the lubricating substances about 
their axles, what will occur when two planets crash to- 
gether? The solidity of the rocks will seem but fluid. 
The planets will melt together with a grinding, crushing 
and heat-developing force which will make them one, and 
will rekindle their extinguished fires. Fusion and even 
the volatilization of portions of the matter must be the 
consequence. To an observer from a distant planet a new 
star would appear. Spectroscopically examined, its light 
would reveal a mixed condition, partly fluid, partly vapor- 
ous; or fluid and vaporous alternately, according to the 
varying character of the luminous matter turned toward 
the observer. Such phenomena have been noted in con- 
nection with the temporary star which appeared in the 
constellation Cygnus in November, 1876. An objection 
to this mode of explaining temporary stars lies in their 
brief duration. A pair of united worlds thus made incan- 
descent would require ages for the dissipation of their 
heat. Such an event would rekindle an extinguished star 
to shine permanently during human epochs; and possibly 
some of our stars are old ones thus relighted. It is still 
possible that the precipitation of smaller masses of mat- 



CONDITIOi^S OF THE FIXED STARS. 517 

ter should originate incandescence of a more temporary 
character. 

(2.) Eruptive action on an incrusting globe. In all 
stages of our earth's incrusted history, the disturbances 
of the crust through tidal action and shrinkage have 
opened outlets for included molten matter. Ever}^ geo- 
logical period has been marked by the outflow of molten 
fluid, to some extent. But the largest escapes of melted 
lava have taken place toward the close of the Tertiary 
Age. American geologists have called attention to the 
vast extent of superficial sheets of ancient lava on our 
Pacific slope;* and Professor Geikie has collected the 
evidences of a similar and apparently contemporaneous 
efllux of lava over northwestern Euroj^e, and regions 
since covered by the North Sea and the north Atlantic. 
In America these lava sheets spread over large areas, 
ranging from the valley of the Columbia River to Arizona 
and New Mexico, and as far east as the Rio Grande of 
Texas. In some places, canons four thousand feet deep 
have been cut through by subsequent erosions. Now, it 
is apparent that when a sheet of glowing lava was spread 
rapidly over hundreds of thousands of square miles, the 
dark planet became again luminous to far distant observ- 
ers. An enormous evolution of gaseous products must 
have accompanied the flow of the lava. The luminous 
phenomena must have endured probably for some weeks 
if not months; but the length of the period of luminosity 
could not have approximated that resulting from the pre- 
cipitation of a planetary body. Now, if an ancient dark- 
ened and incrusted sun or planet should undergo, in the 

* See especially Jos. Lecoute, On the Great Lava Flood of the West, Amer. 
Jour. Sci., III. 167-80, 259-67, March and April, 1874. See also J. D. Whitney: 
Geology of California, and the various Government Geological Keports. There 
are some, also, who still hold to the primitive molten fluidity of all granites and 
many ancient schists. See Address of C. H. Hitchcock at Minneapolis, Science, 
ii, 223-7, 31 Aug., 1883. 



518 FIXED STARS AXD XEBUL.E. 

distant heavens, an experience similar to that which seems 
to have befallen our planet in the later stages of its 
history, there must have been revealed to human eyes a 
spectacle somewhat similar to that which we have wit- 
nessed in the phenomena of "temporary stars." 

(3.) It is also conceivable that a rekindling of a dark- 
ened sun or planet should result from the impact of a 
wandering cometary body. It is even supposable that 
a luminous star, too small or too distant to be visible, 
should be increased in brilliancy by such a collision to an 
extent which would render it visible to human eyes. If, 
however, so great an increase of brilliancy should be 
caused as marks the usual progress of a temporary star 
from invisibility to a star of first magnitude, there would 
seem to be implied a quantity of evolved heat which could 
not be radiated during the ordinary continuance of a 
temporary star. 

I have myself adopted the second explanation as the 
one most probable. Every cosmical body must normally 
pass through the incrustive and eruptive stage ; but we 
are not so certain that every one is destined to a rekind- 
ling through impact of descending matter. 

3. ^^oi'iohJe Stars. — Those stars which alternately in- 
crease and diminish in brilliancy must present some spe- 
cial conditions admitting of correlation with the progress 
of cosmical development. More than twenty of them 
have been shown to possess fixed periods of change, vary- 
ing from about two days and twenty-one hours to 495 
days,* Several of them complete their periods with uni- 
formity reaching to a minute, and even a second, of time. 
Nothing but axial rotation of the body, or orbital revolu- 
tion of an occulting body is conceivable as the basis of such 
punctuality. In some cases, however, as in that of Algol, 
the period is too short to ascribe, with probability, to oc- 

*Argelander, in Humboldt's Cosmos^ iii. 



CONDITION'S OF THE FIXED STARS. 519 

cultations. It is therefore probable that the phenomenon 
is generally due, as Zollner suggested, to rotation of bod- 
ies having sides of different degrees of luminosity. 

But there is also a variable factor in the periodicity of 
most variable stars. The maxima attained are not always 
of the same brightness ; nor are the minima always the 
same. Sometimes the progress toward either extreme is 
marked by stages more or less irregular, and more or less 
differing in different periods. These phenomena point to 
changes in the brilliancy of the light received from the 
same hemisphere. It is highly improbable that these 
irregular fluctuations are caused by the transit of dark 
bodies. There must be variations in the intrinsic lumi- 
nosity of the same regions.* 

Now, the sun is a star near enough for closer study. 
The sun's disc is generally mottled by the well known 
solar spots. The number of spots has recently been shown 
to increase and diminish in a fixed cycle of about eleven 
years. As the solar light must be somewhat diminished 
by the presence of spots, it is apparent that the sun has a 
period of about eleven years. It is not at all improbable 
that the darkening effect of the spots may continue to in- 
crease until the diminution of light at times of greatest 
maculation shall become distinctly marked. With the 
thickening of the photospheric envelope, and the increase 
of resistance to the outbursts of the internal darker gases, 
the violence of the action accompanying the outbursts 
will increase ; just as the most copious outflows of lava 
on the earth's surface took place after the crust had be- 
come comparatively rigid. Our sun would thus be un- 
questionably a variable star ; and it is apparent that the 
initiatory stage of such a condition has already arrived. 
But it is further equally conceivable that maculation might 

* On the causes of the variability of stars see Pickering, Proc. Amer. Acad. 
Arts and Sciences^ xvi. 



520 FIXED STARS AXD XEBUL.E. 

constantly predominate on one side during one or two 
generations of men. Such a condition would give a 
shorter period, determined by the sun's axial rotation. 
Or, variations in the depth of the maculations on the 
brighter or the darker side might cause irregular progress 
toward maximum or minimum brightness. These consid- 
erations applied to the variable stars of our firmament 
would seem to offer a plausible explanation of all the 
phenomena. 

The question whether the variable condition attends 
upon a more or less advanced stage than that presented 
in stars with steady light can only be answered when we 
know the cause of the spots. It is generally admitted at 
the present time, that their existence depends on the out- 
burst, cooling and descent of heated gaseous matters from 
the region within the solar photosphere. Father Secchi, 
speaking of the connection between the spots and the 
protuberances, says: "The spot is formed b}^ the matter 
itself which the eruption projects upon the solar disc. 
The dark region is due to the absorption exerted by the 
vapors issuing from the bosom of the sun and interposed 
between the observer and the photosphere."* The theory 
of Faye differs in supposing the rupture in the photo- 
sphere to result from a vortical disturbance in that layer, 
which carries cooler vapors down ; while Professor Young- 
favors a slight modification of Secchi's theory. All these 
views make the spots depend on the sujDerficial accumula- 
tion of vapors relatively cooler than the photosphere in 
whose depressions they rest. The diminished luminosity 
of the spots is due, therefore, to the high absorptive power 
of their substance ; and this results from a relation of 
temperature. An increased efficiency of the cause or con- 

* Secchi: Le Soleil. 2d ed. 1875-7. ii. 184': See also, Faye, Compter Rendus, 
Jan. 16 and 23, 18(35, and July 27, 1868, Tome Ixviii, p. 197; Newcomb: Popular 
Astionomy, 280-2: Young: The Sun, 128. 175 : Langley, in Xe\vcomb"s Popular 
Astronomy, 280-2. 



CONDITIONS OF THE FIXED STARS. 521 

dition of cooling of the ejected (or accumulated) vapors 
would increase the maculation, and in this view, one 
suggestion would be that excessive maculation marks an 
advanced stage in solar life. But it appears that macula- 
tion is a differential phenomenon. It results from the dif- 
ference in the temperature of the subphotospheric region 
and the region exterior to the photosphere ; and this could 
be greatest by a more intensely heated interior as well as 
by a cooler condition of the surrounding atmosphere. It 
was the opinion of Father Secchi,* nevertheless, that 
maculation is a phenomenon of advanced solar life, and 
that progressive refrigeration must tend to increase it. 
Should this be a true conclusion, our sun is destined to 
become more distinctly a variable star in some future age ; 
and we may regard such stars as Beta of the Lyre and 
Mira of the Whale as more advanced in development than 
our own sun is. This, however, is a question which must 
be left, for the present, little better than a matter of con- 
jecture. Algol, meantime, which varies with exact regu- 
larity and in short periods, is said to be distinctly a star of 
Secchi's first type ; and is to be associated, therefore, with 
Sirius and Vega. Its variability I have thought probably 
ascribable to rotation of a body of different luminosity on 
different sides. 

It was Zollner's suggestion that a variable star is a body 
reduced to a liquid state, with floating slags dimming the 
light on certain sides. This is akin to my suggestion re- 
specting temporary stars, and seems a very rational expla- 
nation. The floating slag, however, should have a more 
fixed position than can be conceived probable unless nearly 
the entire surface has become slag-covered. This, then, 
would be a state of incipient incrustation, while the tem- 
porary star would exemplify an incident in advanced in- 
crustation. 

* Secchi : Le Soleil, ii, 456. 



522 FIXED STARS AND NEBULA. 

4. Gradations of Stars. — Every one has remarked the 
fact that certain stars, like Sirius, shine with a white light; 
others, like Capella, with a yellow light, and still a few 
others, with a ruddy light. Father Secchi showed that 
these three classes of stars afford three classes of spectra. 
As the spectrum depends on conditions of existence of a 
source of light, in reference to temperature, envelopes 
and pressure, the variously colored stars must exist in dif- 
ferent conditions. In order to learn how far the spectro- 
scopic characters of the stars furnish data for coordinating 
them in a genetic series, I present a condensed statement 
of the characteristics of the four or five classes of stars 
pointed out by Father Secchi * in his beautiful work on 
the sun. 

First Type. — This embraces most of the ichite stars, 
such as Vega, Altair, Regulus, Rigel, the stars of the 
Great Bear with the exception of a, those of Serpentarius, 
etc. The class includes about half of the stars. Though 
commonly called white, they are, in reality, faintly blue. 
The remarkable variable star Algol seems to belong here. 
The spectrum in this class presents a group of seven colors 
interrupted by four dark lines, one in the red, another in 
the green-blue and two in the violet. These all belong to 
hydrogen, and coincide with the four brightest lines of 
this gas, when existing at a high temperature. Besides 
these broad fundamental lines, the brightest of these stars 
afford a very fine dark line in the yellow, which appears 
to coincide with sodium; and in the green, some still 
fainter lines which pertain to magnesium and iron. The 
most striking peculiarity of this type of stars is the breadth 
of the hydrogen lines; which tends to show that the ab- 

* Secchi: Le Soleil, 2d ed., ii, 449-01; first aunoimced in 18()7, in Catalogo 
delle Stelle di cui si e determbiato lo Spettro lum'moso air osserva(o)io del Col- 
legia Romano. See the substance of Father Secchi"s views in Schellen: Die 
Spectralanalyse, and the English translation, Am. ed., Spectral Analysis, 342-50. 



COJ^DITION^S OF THE FIXED STARS. 533 

sorbent layer possesses great thickness and exists under 
considerable pressure. 

Second Type. — This embraces the yellow stars^ like 
Capella, Pollux, Arcturus, Aldebaran, Alpha of the Great 
Bear, Procyon, etc. Arcturus, however, approaches the 
third type, while Procyon approaches the first. The spec- 
trum is perfectly similar to that of the sun. This class 
embraces about one-third of all the stars. 

Third Type. — These stars are all variable. In color 
they range from red toward orange. The type includes 
Alpha of Hercules; Beta of Pegasus; Omicron (or Mira) 
of the Whale; Alpha of Orion; Antares, etc. There are 
about thirty of first importance, and one hundred in all. 
The fundamental dark lines are the same as in the second 
type, but there are also present numerous nebulous bands 
which divide the spectrum and make of it a sort of colon- 
nade illuminated from the side of the red. These spectral 
zones depend on variations in the stars, and these depend 
on the more or less absorbent action of their atmospheres. 
At the bottom of the solar spots a spectrum is obtained 
more profoundly rayed, and crossed also by dark bands. 
These stars then appear to ow^e their spectrum to an ab- 
sorption analogous to that produced in the solar spots. If, 
therefore, our sun had everywhere an absorbent layer like 
that exposed in the spots, it would present the same aspect 
as the stars of this class. The most conspicuous lines are 
those of magnesium, sodium and iron. They are rather 
bands than lines, since they are broad, and shaded along 
the edges. This seems to indicate a powerfully absorptive 
atmosphere. There are also fine hydrogen lines, but they 
do not dominate as in the first two typos. This gas cer- 
tainly exists in these stars, but its lines are partially re- 
versed, as happens in the spectrum of the solar spots. 
Most of the dominant lines belong to metals which have 
been found in the sun. 



524 FIXED STAKS AND NEBULA. 

The spectrum is the same as that of the sun — or 
rather Arcturus — but profoundly divided by nebulous 
lines due probably to oxides.' This indicates a tempera- 
ture less than that of the sun. 

The stars of the second and third types seem to differ 
simply in the thickness of their atmospheres, and in the 
discontinuity of the photosphere in the third type. These 
should have, then, variable spots like those of the sun, but 
of vastly greater dimensions, or even completely envelop- 
ing the star, forming a general layer more absorbent and 
less heated. 

Fourth Type. — This consists of about thirty stars of 
blood-red color. The spectrum contains three fundamen- 
tal bright bands, yellow, green and blue, not reducible 
to the preceding type, for the distribution of the light 
is entirely different. They are brightest on the side 
toward the violet, and fade gradually in the opposite 
direction. Some yield a faint trace of red. Some of the 
dark lines coincide pretty well with the third type, but 
the spectrum as a whole is that of a gaseous body rather 
than one of absorption. If considered an absorption 
spectrum, it presents the characteristics of carbon com- 
pounds, such as are yielded when a succession of electric 
sparks is passed through vapor of benzine and atmos- 
pheric air. 

Fifth Type. — This consists of few stars, including 
Gamma of Cassiopoeia and Beta of the Lyre, a variable 
star. It affords a direct hydrogen spectrum. The first 
named, according to Huggins, gives a spectrum in which 
the bright lines Ha (red) and H ^ (greenish blue) are visi- 
ble in the places of the dark lines C and F. A bright 
line in the yellow, in place of D, is also suspected. The 
star Eta Argus gave a spectrum also, in which some of 
the most intense of the nitrogen lines were seen as bright 
lines. Two variable stars have been seen to give also a 



CONDITIOls^S OF THE FIXED STARS. 525 

direct but discontinuous spectrum — one in 1866, in the 
Northern Crown; the other R Geminorum. The tempo- 
rary star in the Swan had also a similar spectrum. It 
seems, according to Secchi, to imply a rapid combustion 
at some former epoch — the light, probably, having been 
many years in reaching us. 

The stars in the constellation Orion present still other 
peculiarities. They belong to the second type in the ex- 
treme fineness of the lines, but are quite exceptional in 
the nearly complete absence of the red and yellow. All 
the stars of this region present a double character: (1) 
They have a very pronounced green tint. (2) Their spec- 
tral lines are so fine that it is difficult to separate them. 
On the contrary, the region of the Whale and the Po 
contains a very large number of yellow stars. This dis- 
tribution, says Secchi, cannot exist by chance. It de- 
pends, undoubtedly, on the nature and the state of the 
substances which fill different parts of the universe. 

No inherent improbability exists that the distribution 
of the different substances is somewhat different in regions 
remote from each other. But we know too much of the 
uniformities pervading the widest regions of space to 
believe that differences of substance can produce any 
fundamental peculiarities such as characterize the various 
types of stars. These peculiarities, in all probability, 
arise from different conditions of tlie common substance. 
There are contrasts of condition, therefore, corresponding 
to the colors of the stars. Whether the different con- 
ditions are successive in the progress of a cosmical evolu- 
tion is an unsolved problem. It may be noted, however, 
that the series of colors, white, yellow and red, is a suc- 
cession presented by successive stages of cooling from a 
white heat. Still, these stages as observed, occur in the 
cooling of a body whose temperature is low enough to 
permit it to retain a solid condition from the first to the 



526 FIXED STARS Ais^P XEBUL.E. 

last; while suns, in all their luminous stages, are supposed 
to be vastly hotter than white-hot iron. Would this suc- 
cession of colors be presented in stages of cooling, all of 
which are far above the temperatures of molten iron ? Or, 
is the supposition erroneous that all the stellar matter 
determining the color of the light is so intensely heated? 
There is a time in the history of a sun when intense 
heat has resulted from the gravitational condensation of 
its parts. Most of its substance exists in a gaseous or 
even dissociated condition. It is improbable that a high 
degree of luminosity characterizes such matter. But the 
peripheral region must always experience important 
effects from radiation. It seems very improbable that the 
general temperature of the mass could be so high or so uni- 
versally distributed that the surface should not be chilled 
to the point of formation of fire mist. A zone of fire mist 
would envelop the gaseous globe like a skin. Fire mist 
is simply gas cooled till minute liquid particles come into 
existence which float in a common atmosphere of gases 
not yet condensed. In the liquid or solid state, lumi- 
nosity is greatly increased, even at a lower temperature. 
In such a zone of fire mist, a circulation of particles must 
be in active progress Coalescence of particles, as in a 
cloud of aqueous vapor, would give rise to drops which 
would descend like rain to tlie lower surface of the photo- 
spheric fire mist. They would even penetrate the hotter, 
gaseous nucleus for a limited distance, but would soon be 
dissolved to gas and returned to the zone of the fire mist. 
By this process, long continued, this photosphere would 
be deepened, and the nucleus correspondingly diminished 
in volume. In the course of time, the nucleus would be 
w^holly replaced by fire mist ; and then would begin that 
central accumulation of a liquid core of which I have else- 
where spoken. The proper life of a sun is therefore divided 
into two stages, in the first of w^iich a gaseous nucleus 



coxditio:n"s of the fixed stars. 527 

goes on diminishing-, and in the other of which a molten 
nucleus goes on increasing. 

But in either stage, the photospheric zone is reduced to 
the point of liquefaction of a considerable proportion of 
its substance. Being liquefied, its temperature must be 
such as is compatible with the existence of matter in that 
state. According to this reasoning, the condition of the 
photospheric particles might be compared with that of a 
mist of molten iron. It might possess the temperature 
and the luminosity which belong to terrestrial substances 
at the temperature of a white heat. The deeper portions 
of the photosphere, however, must be more copiously per- 
vaded by a gaseous medium at a higher temperature; and 
the entire gaseous nucleus, so far as I perceive, may sub- 
sist at any temperature compatible with the evidences 
bearing on the intrinsic heat of solar bodies. 

But if the particles upon the outer surface of a photo- 
sphere ma}' exist at the temperature of the white heat of 
molten iron, it seems possible they may also exist as solid 
particles at the lower temperature which emits a yellow, 
or even a ruddy, light. In this view, the colors of the 
stars may truly denote successive stages in a process of 
cooling. Whether such a conclusion is compatible with 
the evidences on which scientific opinion has generally 
agreed to ascribe a much higher temperature to the sur- 
face of the sun, is a question for the future to decide. 
It will be noticed, however, that the general heat of the 
solar surface is constituted partly by the higher tempera- 
ture of the gaseous medium from which the photospheric 
particles are generated. This may also be added, that on 
most of the solar bodies the enormous force of gravity 
would have the effect of raising the point of liquefaction 
from a gas, and the enormous pressure of the superin- 
cumbent atmosphere, however rarefied by heat, would in- 
crease this effect; so that the incipient molten stage 



528 FIXED STARS AND N-EBUL^. 

would imply a higher absolute temperature than on the 
earth. It is still true that the lower limit of luminosity, 
and probably all higher degrees of it, would be deter- 
mined by the rate of molecular vibration, independently 
of the condition of the matter as to fluidity. For this 
reason nearly all substances might require an intense 
white heat even for liquefaction, and a vastly higher heat 
for conversion into the less luminous condition of gaseity. 

In view of the whole range of considerations, T shall 
assume provisionally that the various colors of the stars 
exhibit a gradation in the cooling process. 

A few further obvious suggestions may be made in this 
connection. In the earliest stages of photospheric exist- 
ence, the fire-mist film would be so thin as to possess 
a lowec degree of luminosity than at a later stage. The 
light emitted would be thin and leaden in hue. It is 
quite conceivable, also, that causes may exist in particular 
cases, for changes in the hue of the light resulting from 
diminished, as well as increased, depth of the photo- 
spheric zone. A star, at one time j^ellow, might recede to 
the white stage. A white star might recede to the bluish 
or leaden stage by increase of its general temperature. 
Thus, it is possible the reputed changes in the colors of 
certain stars, which are of a retrogressive significance, 
may be interpreted in harmony with the provisional con- 
clusion which I have enunciated respecting the meaning 
of color gradation among the stars. 

But, if we admit that the white, yellow and red colors 
of the stars represent as a general, though not invariable 
rule, successive cooling stages, it remains to ascertain 
whether these stages all appertain to photospheric life, or 
characterize, in part, the later stage, incandescent incrus- 
tation; and also, whether, if one or all of them apper- 
tain to photospheric life, it is that period which precedes 
or follows the beginning of liquid nucleation. We dis- 



CONDITIONS OF THE FIXED STARS. 529 

tinguish three phases in the life of a self-luminous cosmi- 
cal globe: (1) The gaseous-nuclear phase; (2) the liquid- 
nuclear phase; (3) the incrusted phase. During the first 
two, or characteristically solar, phases, a photosphere 
exists, consisting of particles of liquid or solid matter, 
and giving by itself a continuous spectrum; but an ab- 
sorbent atmosphere still existing in abundance, the result- 
ant spectrum is crossed by dark lines. The volume and 
density of the enveloping atmosphere are so great that 
the dark lines possess a greater breadth than in the solar 
spectrum. During the third phase, the spectrum should 
be continuous; but still, at the supposed temperature, a 
dense, heterogeneous and absorbent atmosphere might 
still impress dark lines upon the bright continuous spec- 
trum. Now, the spectral conditions of the first two stages 
are exhibited by the white and yellow stars — the white 
stars giving the broadest dark lines, and thus evincing the 
greatest depth of atmosphere. We must conclude that 
these two stages belong to the photospheric period. The 
indications of the few red stars are ambiguous. Their 
spectrum is characterized by dark lines, but Father Secchi 
was of the opinion that they offer some indications of 
more predominant gaseity than the others. Their red 
color may result from some other cause than their ad- 
vanced stage of cooling. But since the incrusted state 
must be accompanied still by a voluminous envelope of 
gases, and since ruddy light is certainly expressive of 
diminished incandescence, while further, the light of the 
crust, with diminished intensity, would be less able to 
contend with the absorbent and luminous powers of the 
atmosphere, I shall venture to assume, though provision- 
ally, as before, that the ruddy stage is generally to be 
interpreted as the early incrusted phase. 

The variable ruddy stars will represent earlier phases — 
sometimes an advanced macular condition, and in some 



530 FIXED STARS AXD XEBUL^. 

cases a phase of incif)ient incrustation; while the tem- 
porary stars are phenomena of advanced incrustation. 

5. Indications of Incipient Stellation. — Certain phe- 
nomena presented by celestial objects not recognized as 
well formed stars may be interpreted as characteristics of 
incipient stellation. Certain dense star clusters, as well 
as most of the so-called resolvable nebulae, present con- 
tinuous spectra. Such a spectrum is yielded by incandes- 
cent solid or liquid bodies. When such a body is sur- 
rounded by gases of low^er temperature, dark absorption 
lines appear in the spectrum; but if the surraunding gas 
itself is intensely heated, it imparts its own bright lines 
to the spectrum, and these then appear superposed over 
a continuous spectrum. But there is a certain intermedi- 
ate state of luminosity in the envelope in which its 
absorbent power is just neutralized by its emissive power, 
and its effect on the spectrum of the inclosed molten 
material disappears. Such seems to be the condition of 
the gaseous medium in the star clusters and resolvable 
nebulas referred to. 

At an earlier stage, the emissive property of the heated 
atmosphere preponderates, and the spectrum is one of 
bright lines over a continuous spectrum. The preponder- 
ance in the emissive power of the gaseous medium may 
depend on the relatively low temperature of the enveloped 
portions; and this may depend on the comparatively low 
degree of condensation as yet attained. A later period, 
therefore, would witness a greater degree of condensation, 
intenser central heat, and a relatively more, powerful lumi- 
nosity. That is, a more advanced stage would increase 
the amount of fire mist and its relative luminosity, besides 
reducing the volume and pressure* of the envelope, and 
thus establish those relations which produce a continuous 
spectrum crossed by the dark lines of an absorbent me- 
dium. This description of spectral power is possessed by 



COSMOGOiq-IC CONDITION'S OF :n'ebul^. 531 

*' Planetary Nebul;i?" and "Nebulous Stars." We may, 
therefore, unite with Sir William Herschel in considering 
these forms as stages of cosmical development, showing a 
passage from nebular to stellar life. * 

§ 2. COSMOGONIC CONDITIONS OF NEBULA. 

Le monde s'elargit done a, nos yeiix; le systeme solaire ne nous pafait plus 
que comme un point dans Tespace. Quelle difference entre ces idees si larges 
et celles qui autrefois liniitaient le monde au notre globe. * * * II est prob- 
able que la reunion des grands etoiles qui environnent notre Soleil n'est qu'un 
des amas qui forinent la Voie lactee, et que vu d'une certaine distance, cct amas 
apparaitrait comme nne tache plus blanche dans la Voie lacte'e elle-meme.— 
Secchi. 

The typical nebula is one which is irresolvable and 
shines with a faint light, affording a spectrum of one or 
more bright lines. The brightest of these lines, with a 
wave length of 5,005, is coincident with a nitrogen line. 
The second, when others exist, has a wave length of 4,957 
(Angstrom). The other two are coincident with hydrogen 
lines H /? or F and H y near G. This spectrum is some- 
times superposed on a faint continuous spectrum. 

In some careful investigations recently made upon the 
nebula in Orion by Mr. Huggins* a fifth relatively strong 
line was observed in the ultra-violet, of wave length 3,730, 
which ap23eared to correspond to C in the typical spectrum 
of white stars. t Mr. Huggins states, also, that he cannot 
say positively that the hydrogen lines between H y and 
the fifth nebular line are wanting, and he even suspects 
their j^resence, as also others beyond the fifth nebular line. 
Mr. Huggins further says, that outside of the usual 
stronger continuous spectrum, which he attributes to stel- 
lar light, he suspects an exceedingly faint trace of a con- 
tinuous spectrum. Dr. Draper's photographs show also a 
continuous spectrum from two condensed portions just 

* Proc. Boy. Soc. March 16, 1882, Nature, xxa-, 489. 
\Phil. Trans., 1880, p. 677. 



532 FIXED STAKS AXD I^EBUL^. 

preceding the trapezium. These observations show the 
nebular spectrum to be less simple than had been supposed, 
and demonstrate, apparently, the presence at least of 
nydrogen and nitrogen. Frankland and Lockyer have 
shown that the spectrum indicates a lower temperature 
than exists in our sun, and a remarkably low density. 

The presence of bright lines indicates that an important 
portion of the nebula is gaseous, while the faint contin- 
uous spectrum, when present, seems to indicate the exist- 
ence of incandescent solid or liquid matter. Though Mr. 
Huggins, an eminent authority, inclines to attribute the 
continuous spectrum to stellar light, I see no strong rea- 
son in the phenomena for denying that both solid and 
liquid matter exist in a luminous condition in most nebulae. 
Assuming, as I have done, that nebular history begins 
with the aggregation of cold matter, some of which is 
analogous to that forming meteoroidal trains, there would 
naturally arrive a time when, by collision of hard constit- 
uents, and condensation of gaseous constituents, heat 
would be developed. This would sooner or later originate 
gaseous luminosity; and this is the typical condition. 
But from this, by peripheral condensation, must arise some 
amount of fire mist; and the very process of volatilization 
implies also a stage of fusion passed. This fire mist, and 
this antecedent liquidity would afford the continuous spec- 
trum. The double spectrum is shown not only in some 
continuous nebula?, but also in a small number of nebulous 
stars. Some nebulre, as heretofore stated, seem to undergo 
a process of segregation of parts by curdling and accumu- 
lation apparently around nuclei. They become then clus- 
ters of nebulous stars. Certain so-called resolvable nebuhi? 
present this condition. This seems rather a collateral 
than a consecutive phase, since, as I have before indicated, 
it may be regarded as characterizing nebulge which do not 
rotate and annulate. 



COSMOGON"TC CONDITIONS OF NEBULA. 533 

Finally, we have to consider a prenebular stage. Be- 
fore the matter of the nebula is collected in form it must 
exist in a formless or chaotic stage. I have already de- 
scribed the phenomena which I suppose to be connected 
with prenebular conditions. The matter is diffused; it is 
cold; it is composed of mineral substances aggregated in 
masses, at least in part, which are drawn together by 
mutual attractions, forming distinct groups or swarms 
which are further aggregated successively, until those vast 
fields of cosmical stuff are accumulated which become 
luminous nebuljB,* Perhaps generally the aggregation 
into masses is very limited, and the matter exists mostly 
as widely scattered particles or molecules. This diffused 
and unorganized condition of primitive world stuff answers 
to the chaos conceived by Kant, though he banished it 
from the realm in which cosmical organization has taken 
place, while the present conception supplies all the spaces 
in the midst of the worlds with these seeds of cosmical 
organization. 

I am not aware that it is possible to trace inductively 
the history of world formation to any remoter point. It 
is certainly possible to conceive these cosmical atoms as 
arising out of some transformation of the ethereal medium, 
and more than once expression has been given to such a 
speculation. f But we know too little of the nature of 
ether to ground a scientific inference of this kind; and we 
certainly have no knowledge or concejDtion of any con- 
dition of matter antecedent to that in which it possesses 
resistance, weight and inertia. The attempt to go farther 
involves us in speculations of a metaphysical character 
respecting the ultimate nature of matter, and this is a field 
of inquiry which it is not proposed to enter. 

* See more specifically, Part I, ch. i, § 7. 

t See the references pp. 49, 50, 61. A later article by A. S. Herschel appears 
in Nature, xxviii, 294-7, July 26, 1883. 



CHAPTER II. 
THE COSMIC CYCLE. 

Facies totius Universi, quamvis infinitis modis variet. nianet tamen semper 
eadem.— Spikoza. 

Herscbel, en observant les nebuleuses an moyen de ses puissans telescopes, a 
suivi les progres de leur condensation non snr nne seule, ces progres ne pouvant 
devenir sensibles pour nous, qu" apres des siecles; mais sur leur ensemble, 
comme on suit dans nne vaste foret Taccroissemeut des arbres, sur les indi- 
vidus de diverses ages, qu'elle renferme.— Laplace. 

§ 1. THE KEYS OF COMPARATIVE GEOLOGY. 

THE views presented in the foregoing chapters direct 
attention to some of the sublimest considerations 
which can occupy the human mind. We rise from the 
contemplation of the interests and affairs of the indi- 
vidual or of the human race, not alone to that larger 
scope of events which constitutes the lifetime of the 
habitable globe w4iich endures while generations and na- 
tionalities come and disappear; but that grander concep- 
tion of the cycle of events which constitutes the round of 
evolutions awaitino; everv ao-o-reo-ation of cosmic matter 
in the material universe. I wish to impress this thought 
of the unity of cosmical history, and lead my reader to 
an impressive apprehension of the vastness of the scheme 
to which he belongs, and of the exaltation of constituting 
a part of a scheme so vast. 

The possibility of rising to a comprehension of a sys- 
tem of coordination so far outreaching in time and space 
all range of human observation, is a circumstance which 
signalizes the power of man to transcend the limitations 
of changing and inconstant matter, and assert his superi- 

534 



THE KEYS OF COMPARATIVE GEOLOGY. 535 

ority over all insentient and perishable forms of being. 
There is method in the succession of events, and in the 
relation of coexistent things, w^hich the mind of man 
seizes hold of; and by means of this as a clew, he runs 
back or forward over asons of material history of which 
human experience can never testify. Events germinate 
and unfold. They have a past which is connected with 
their present, and we feel a well justified confidence that 
a future is appointed which will be similarly connected 
with the present and the past. This continuity and unity 
of history repeat themselves before our eyes in all con- 
ceivable stages of progress. The phenomena furnish us 
the grounds for the generalization of two laws which are 
truly principles of scientific divination^ by which alone 
the human mind penetrates the sealed records of the past 
and the unopened pages of the future. The first of these 
is the law of evolution, or, to phrase it for our purpose, 
the laio of correlated successiveness or organized history/ 
in the individual, illustrated in the changing phases of 
every single maturing system of results; as organic struc- 
ture, human civilization or world-growth. The second is the 
law of correlated siimdtaneoiisness, or parallel history in 
many individuals, whereby many particular instances of 
progressive development in different stages of maturity 
are presented simultaneously; as the different persons in 
a large city exemplify simultaneously the stages of devel- 
opment attained by any individual on every day of his life. 
Thus, by virtue of these two laws, each individual under- 
going an evolution finds at every moment its entire past and 
future recorded in the present of other individuals belong- 
ing in the same category. The man of mature years can 
turn in one direction and study the stages which he has 
passed through from earliest infancy; and in the other di- 
rection, the stages which, in the course of nature, he will 
pass through to remotest old age. I go into the forest, and 



536 THE COSMIC CYCLE. 

within an hour trace the life history of an oak all the way 
from the acorn to the crumbling veteran of three hundred 
years. An ephemeron intelligence could thus write the his- 
tory of a tree destined to endure a thousand years. It is 
so in the history of a planet. Man is an ephemeron com- 
pared with the lifetime of a world; but while he endures, 
he notes thousands of worlds in all the different stages 
of world-life, and, selecting a series of examples, he runs 
them on a continuous thread, and has a tale of evolu- 
tions which span a million years. Individual histories 
have begun at different periods in the lapse of time; and 
individual histories, whether simultaneously begun or not, 
have been accelerated or retarded by differences in the 
modifying conditions. 

Our earth has reached a certain stage of development. 
It happens at this epoch ^to be a habitable world. It is 
supposable that its present state has persisted from eter- 
nity; and this was the belief of some of the ancients, as 
well as a few of the moderns. Limited observation, how- 
ever, shows that changes are taking place — that a history 
is in progress, and the mind demands the past of this his- 
tory — that which lies back of the observation of the 
individual, or even of the race. Now, availing ourselves 
of the lav: of parcdlel history, we study the phenomena 
of beach erosion and detrital accumulation, and see in 
these a picture of Silurian times — of geologic changes 
consummated thousands of years before even our race had 
an existence. This is pure geology. But nothing in the 
existing phases of the planet can reveal -the history of 
events which transformed the planet. Bodily transfor- 
mations obliterated all records of what was past. Ge- 
ology has perpetuated terrestrial history only by the fixed 
forms of enduring rocks. But we find in igneous masses 
intimations of an older state, whose records were written 
upon fluid matter, to be inevitably effaced. Here is the 



THE KE^S OF COMPARATIVE GEOLOGY. 537 

limit of possible geology. But we learn that our earth, 
as a whole, is but one of a series of planets; that these 
planets, from their common physical relations, must have 
had a common history; that before they were planets, 
they belonged to a category of existence of which the 
sun is a type and a remnant; that, probably, in some 
remoter epoch in the past eternity^ all the suns belonged 
to a category of existence now exemplified in irresolvable 
nebulae; and we learn that all these conditions are phases 
in the consummated history of our world — that the 
investigation of them is at the same time cosmogony and 
geology. 

The fundamental data of this comparative science of 
world growth have been already passed under review.* 
The first group of data unites the earth, the planets and 
the satellites in a single category of existence. The com- 
munity of movements, forms and conditions is such that 
we feel borne to the conclusion that whatever may be de- 
termined as to the past or future conditions of our world 
must be also conditions in the life history of each of the 
other planets. These relations have arrested the atten- 
tion of* all students of nature, and have produced in the 
most thoughtful minds an irresistible conviction that the 
members of the Solar System constitute but one family 
— that all the planets and satellites must have had a com- 
mon starting point. This conviction has found expres- 
sion in the theories propounded by Kepler, Newton, 
Leibnitz, Kant, Herschel and Laplace. 

The most recent results of speculation concerning the 
progress of cosmical evolution I have set forth in preced- 
ing chapters. It will be of interest now, to glance from 
our elevated standpoint over the whole realm of cosmical 
existence and note synoptically the stages attained by the 
different orders of worlds in human times, and then to 

* Part II, chapters i-iv. 



538 THE cos:mic cycle. 

follow the current of events onward from our present ter- 
restrial condition toward some far-off cosmical finality.* 

§ 2. TPIE FIXAL GEXERALIZATIOX. 

Alles was endlich ist, was eineu Anfaug mid Urspruug hat, hat das Merknial 
einer eingcschrankten Natur; es muss vergehen und ein Ende haben.— Kant, 

1. Stages of World-life. — The deepest principle of 
change in cosmic existence is exjDressed by the word eool- 
ing. The broadest physical generalization to be drawn 
from the phenomena of the cosmical realm is the affirma- 
tion of progressive reduction of temperature. The his- 
tory of a world is a history of cooling. All other world- 
making activities come into play concomitantly. If the 
process of cooling transforms also a vast amount of me- 
chanical energy into the form of heat, it is always, and 
necessarily, less in amount than the energy lost in trans- 
forming it. 

The three great cosmic forces are liecU and atomic and 
molar attractions. To these should probably be added 
repulsions. 

A world's lifetime, with its incidents and consequents 
is but a progressive cooling. Every individual world in 
the established order of events, passes or may pass, suc- 
cessively through all the stages and phases known to 
cosmogon3\ Cosmic lifetimes have begun at different 
epochs, and proceed at different rates of change. Some 

* The present writer's first published attempt to generalize the whole course 
of cosmical history was a brochure entitled The Geology Qf the Stars, 32 pp., 
12mo, Boston, 1872, being No. 7 of "Half Hour Recreations in Popular Science," 
pp. 255-286. Almost simultaneouslj"^ appeared Mr. Stanislas Meunier : Le del geo- 
logique, inodrome de Giologie Compane, Paris, 1871. A descriptive treatment of 
the early and remote future history of our world, with glimpses of the compara- 
tive geology of oar system was presented by the writer in Sketches of Creation, 
12mo, pp. 459, with illustrations, New York, 1S70. He has also discussed the 
subject in Tlie Unity of the Physical World, Part I, Facts of Coexistence, 
Part II, Facts of Succession, Meth. Quarterly Review, April, 1873, and Janu- 
ary, 1874. 



THE FI:N'AL GEi^ERALIZATIOI^". 539 

began so far back in eternity or have proceeded at so 
rapid a rate, that their careers are brought to a conclu- 
sion in the passing age. Some are even now awaking into 
existence ; and it is probable that worlds are beginning 
and ending continually. Hence cosmic existence, like the 
kingdoms of organic life, presents a simultaneous pano- 
rama of a completed cycle of being. A taxonomic 
arrangement of the various grades of animal existence 
presents a succession of forms which we find repeated in 
the embryonic history of a single individual, and again 
in the succession of geological types ; so the taxonomy 
of the heavens is both a cosmic embryology and a cosmic 
palaeontology. 

In endeavoring to present by way of resume, a syste- 
matic or developmental arrangement of cosmical condi- 
tions, our thoughts fix at once npon four general stages 
of world-life. These are first, the Chaotic or Prenebular ; 
second, the Nebular Stage ; third, the Solar Stage ; and 
fourth, the Planetary Stage. Under the last three we may 
readily discriminate several phases of progress. It prob- 
ably is not possible, in the present state of human knowl- 
edge, to arrange these phases in a final consecutive order. 
Probably some phases are parallel with others, instead of 
consecutive. Nevertheless, a developmental arrangement 
is a desideratum ; and the inexpert reader will be thank- 
ful for a systematic exhibit of the best results science has 
as yet attained, or even for the following resume of the 
discussions and conjectures ventured upon in the present 
work. 

I. CHAOTIC STAGE. 

Cosmical dust. Cosmical atoms promiscuously dis- 
persed in space ; gathering themselves in groups large 
and small ; forming meteors, meteor oidal trains and prob- 
ably comets^' in their larger aggregations becoming- 
nebular dust, either cold or partially heated. 



640 THE COSMIC CYCLE. 

II. NEBULAR STAGE. 

1. Normal Nebular Phase. — Faintly luminous matter 
consisting perhaps of mineral mist formed of incandes- 
cent liquid or solid particles floating in a luminous, gas- 
eous medium, or of stony particles and masses whose 
mutual collisions develop heat and incandescent gases. 
Spectrum consisting of one, two, three or four bright 
lines, or perhaps of five or more, revealing the presence of 
nitrogen and hydrogen, and sometimes superposed on a 
faint continuous spectrum. Density low and heat less 
than that of our sun. Exemplified in certain irresolvable 
nebulae. 

Note. — The thermal incandescence of the normal nebula remains 
to be fully established. 

2. Nebular Fire 3Iist. — Mineral m.ist increased in quan- 
tity, but a gaseous medium still predominant. Condensa- 
tion and evolution of heat in progress. Spectrum of 
bright lines superposed on a faint continuous spectrum, 
showing presence of fire mist, 

A. Continuous fire mist. The nebular mass remains homogen- 
eous and its luminous constituents mostly gaseous. Certain 
irresolvaUe nebulae, as H. 4,374. Also a small number of 
stars, as Gamma of Cassiopoeia and Beta of the Lyre. 

Annulations perhaps begin in this phase. The primitive 
nebula may thus be resolved into solar nebula? in which other 
annulations succeed; or if the mass is insufficient, it may 
proceed with only the evolutions of a solar nebula. Annular, 
and probably spiral and falcate nebulae belong here, the two 
latter illustrating a disturbed state of annulation. Satur- 
nian rings persisting like a preserved embryo. exempHfying 
the form but not the stage. 

B. Discontinuous fire mist. Phase parallel with A. Xebula un- 
dergoing segregation and accumulation around local nuclei 
without annulation. Also, entire nebulae slowly condensing 
around single nuclei. Certain resolvable nebulce (compare 
nebula in Draco). 

3. Nucleating Phase. — Distinct central condensation. 



THE FIKAL GENEEALIZATION. 541 

Photospheric matter increased, but the gaseous medium 
predominant. Bright Hnes over a continuous spectrum. 
Sun systems and planetary segregations past the stage of 
annulation. Planetary nebulm, especially H. 838, H. 464, 
H. 2,098 and H. 2,241.* Also Nebulous Stars, as H. 450. 
4. Nucleated Phase. — Condensation more advanced. 
Temperature and luminosity of the fire mist so increased 
that the absorbent power of the gaseous atmosphere is 
precisely neutralized and the spectrum is continuous. 
Point of transition from bright-line spectra to dark-line 
spectra. Phase observed probably, in certain star clusters, 
and most resolvable niibulce. 

XoTE. — The continuous spectrum may, in some cases, be only 
apparent, the fineness of the lines rendering them invisible with exist- 
ing instruments. 

III. STELLAR STAGE. 

1. Sirian Phase. — Increased condensation and in- 
creased heat. Atmosphere increased in volume and ten- 
sion. Absorbent capacity exceeds the emissive. Spec- 
trum continuous and crossed by four dark lines having an 
extraordinary breadth. White Stars (Secchi's First Type). 

XoTE. — The mass of the star, independently of its age, would in- 
fluence the tension of the absorbent medium, and hence the width of 
the dark lines. We cannot be certain, therefore, from spectroscopic 
indications, that this phase precedes the next. Guided by color 
alone, the white stars should precede the yellow. 

2. Capellar Phase. — i\.bsorbent atmosphere reduced 
in depth and consequent tension, to such an extent as to 
give very numerous dark absorption lines of normal 
breadth. Spectrum identical with normal spectrum of the 
sun. Yellow Stars (Secchi's Second Type). 

Some fixed stars in the last two phases, the centres of 
cosmic systems. Some have attendant worlds still lumi- 
nous. Sirius is a sun with four still luminous planets. 

* These designadoiis refer to Herschel's Catalogue of Nebulae. 



542 THE COSMIC CYCLE. 

Procyon, Higely Aldebaran, Arctiirus, Antares^ C Ca7i- 
cri, etc., have each one or more. Some of these com- 
panions have still smaller attendants, as jx Liqyi, r^ LyrcG, 
c Cancri, 12 Lyncis, d Orioiiis. These are still luminous 
satellites. 

3. Solar Phase. — Photospheric matter copious. At- 
mosphere in a high state of activity, and still causing a 
spectrum of dark lines. The heated nucleus ejecting 
gases through the photosphere, which fall back, on cooling, 
and form dark spots on the surface of the j^hotosphere. 
Incipient variability. 

A. Phase of the gaseous nucleus continually diminishing. 
Probably our own sun. 

B. Phase of the molten nucleus continually increasing. This 
succeeding phase A. 

4. Variable Phase. — Photosphere periodically dark- 
ened by the condensation of large amounts of macular 
matter. Probably approaching total liquefaction. Spec- 
trum as in Second Phase, but with numerous nebulous 
bands brightest 07i the side toicard the red. Periodic and 
Irregular Stars '(Secchi's Third Type). Some variable 
stars probably advanced to incipient incrustation. 

5. 3Iolten Phase. — Photospheric matter exhausted by 
precipitation. Absorbent media greatly reduced. A mol- 
ten globe. Spectrum continuous. Probably some of the 
Star Clusters and Resolvable N^ehidce. 

6. Incrustive Phase. — Early periods of incrustation. 
The light becomes ruddy. Incipient darkening. Spectrum 
of dark lines, but crossed by three bright bands, brightest 
on the side toward the violet. Red Stars (Secchi's Fourth 
Type). 

Note. — I am much in doubt concerning the proper position of 
the "red stars." Their spectra, unless some explanation can be 
given, would place them between the Xebiilar and Stellar Stages. I 
assume, therefore, that the early incrustive phase is one which pre- 
sents the reproduction or fresh disengagement, of some enveloping 



THE FIKAL GENERALIZATION". 543 

absorbent medium. I have already recorded my conviction that it 
is a phase of aqueous condensation and aqueous gaseity — the pre- 
hide of the stormy period. 

7. Eruptive Phase. — Crust so darkened as to be invisi- 
ble as a star; but disrupted at intervals, giving spasmodic 
luminosity, which shines through an atmosphere of aque- 
ous vapor and gas. Spectrum continuous, and crossed by 
dark lines like the solar spectrum, with a superposed 
spectrum of four bright lines. Temporary Stars, also y 
Cassio2)ceue, i3 Lyrc^i (variable) and -q Argus (Secchi's Fifth 
Type). 

Note. — The phenomena of a temporary star may recur many 
times during the progress of the planetary phases, and thus give the 
star a remotely periodic character.* 

IV. PLANETARY STAGE. 

1. Jovilan Phase. — The incrustive phase has passed 
into the stormy phase. A water mist condenses in the 
peripheral regions, as formerly the fire mist appeared. It 
gathers into a vaporous envelope constituting a true atmos- 
phere or nephelosphere. This precipitates an aqueous 
rain, the homolog-ue of the molten rain of earlier times. 

A. Phase of fading luminosity. Crust not yet darkened or cool 
enough to receive the rains. Phase of Jupiter. 

E. Phase of the primeval ocean. Protophytic and later, proto- 
zoic life, on planets otherwise suitably conditioned. 

2. Terrestrial Phase. — Aqueous precipitation periodi- 
cal. Cyclonic movements of the atmosphere, perhaps the 

* The writer is fully aware of the insufficiency of the known data for corre- 
lating the various phases of cosmical matter, and of the rashness of his own. 
attempt to do what has not been attempted by the masters of stellar physics. 
We need to know much more yet respecting the relations of spectra to tempera- 
ture, pressure and molecular arrangement; and also, in view of the analogies 
drawn from light in Geislerian tube.?, more of the connection between the ten- 
sion of the electric current and the temperature and density of the gas made 
luminous by the electric discharge. The reader, nevertheless, who will avoid 
placing too much stress upon the details of the foregoing arrangement, will ob- 
tain a correct impression of the great fact of progressive changes in cosmical 
matter. 



544 THE COSMIC CYCLE. 

homologues of those which cause solar maculations. Period 
of organic life, embracing its culmination. The Earth, 
and possibly Ve7i}is and some of the satellites of Jupiter. 

3. Martial Phase. — Planetary senescence. Dimin- 
ished vapors and infrequent rains. Encroaching cold. 
Decline of organic development. Mars, and possibly the 
Jovian satellites. 

4. Synchronistic Phase. — Tidal retardation of rotary 
motion progressing, and reaching its finality. Moon, and 
probably all the older satellites. 

Note. — This is not a true consecuth^e phase connected \vith the 
progress of inherent or developmental change, but a state growing 
out of relations to other bodies. It may be reached sooner or later, 
according to the efficiency of the tidal action exerted. 

5. JLunar Phase. — Planetary death. Disappearance 
of aqueous vapors and total absorption of water and at- 
mosphere. Extinction of organization. Final refrigera- 
tion, exemplified in the 3foon. In bodies with an excess 
of water and air, the surface becomes ice-covered and the 
copious atmosphere remains laden with frozen vapors. 
Saturn, Uranus and Neptune and their satellites. 

However conjectural some parts of the foregoing ar- 
rangement may be, there is little doubt that its general 
tenor expresses a fact in the aspects of the universe. This 
I have endeavored to explain and impress. We know 
enough of the phases of matter in the different provinces 
of space to feel certain that they represent progressive 
stao-es in the natural evolution of matter as such. Whether 
seen in nebula, star, sun, planet or satellite, it is a phase 
in a common histor}^, the earliest periods of which are as 
truly a part of the history of our world as the achieve- 
ments of Alfred the Great are a part of the history of 
communities of American birth. 

6. Some Final Deductions. — These views are calcu- 
lated to produce upon our minds a profound impression of 



THE FINAL GE]!q"EKALIZATIOX. 545 

the unity of the universe, both in its spatial extent and its 
historical development. When we combine with these 
evidences the indications of the presence of a common 
ether or other luminiferous medium, and of the supremacy, 
everywhere, of the universal law of gravitation, we are 
placed in possession of an overwhelming demonstration of 
the identity of the government which controls natural 
events upon our planetary abode, and in departments of 
space so remote that light occupies hundreds of years in 
traversing the distance. Whatever intelligence, power or 
goodness may seem to be exemplified in the ordinations of 
terrestrial affairs, is not less certainly illustrated in the 
phenomena which we trace to the utmost verge of the 
visible universe, and to the remotest conceivable com- 
mencement of material history. The intelligent Power 
whose supreme control is recognized within the narrow 
limits of personal experience is one through stretches of 
space and time which, to human faculties, are infinite. 

The study of stellar geology leaves us with another 
reflection. Every phase of matter seen in the universe is 
a transient one. The various phases sustain demonstrably 
some sort of historical relation to each other. These 
states of matter are progressive. We trace them back- 
ward toward earlier conditions — toward an earliest con- 
dition, beyond which we know no possibility of cosmical 
existence. From that condition to the present is but a 
finite career, however vast the interval appears expressed 
in numbers. The history began in time; it does not come 
down, to us from eternity. The material orgcmisin is, 
therefore, originated in time. Now, when we carry our 
thoughts back to that primal condition indicated, we must 
necessarily perceive that it existed absolutely unchanged 
and unprogressive from all eternity, or the matter itself 
which exemplifies it did not exist from eternity. But we 
have not the slightest scientific ground for assuming that 



546 THE COSMIC CYCLE. 

matter existed in a certain condition from all eternity, 
and only began undergoing its changes a few millions or 
billions of years ago. The essential activit}" of the pow- 
ers ascribed to it forbids the thought. For all that we 
know — and, indeed, as the conclusion from all that we 
know — primal matter began its progressive changes on 
the morning of its existence. As, therefore, the series of 
changes is demonstrably finite, the lifetime of matter itself 
is necessarily finite. There is no real refuge from this 
conclusion; for, if we suppose the beginning of the pres- 
ent cycle to have been only a restitution of an older order 
effected by the operations of natural causes, and suppose 
— what science is unable to comprehend — that older 
order to be a similar reinauguration, and so on indefinitely 
through the past, we only postpone the predication of an 
absolute beginning, since, b}^ all the admissions of modern 
scientific philosophy, it is a necessity of nature to run 
down. No former condition is completely reproduced. 
The total energy in the cosmic organism diminishes. A 
finality is impending, and hence a past eternity would 
have sufficed to reach it an eternity since, and we should 
not be witnesses of the continued progress of events. 
Whatever process from an infinite beginning involved an 
end is now a process ended, not continuing. The conclu- 
sion is unavoidable that the cosmic organism began in 
time, and that the very existence of matter is limited in 
the past. 

The dependent existence and finite origin of matter 
are revealed in its ultimate constitution. The scenes 
which we have been contemplating are characterized by 
ceaseless nutation and transformation. The very notion 
of an evolution presupposes this. The progressive activ- 
ity of nature's forces continually rebuilds the material 
organism. The old disintegrates and reappears trans- 
formed. Nothing is jDermanent. The ponderous forms of 



THE FINAL GENERALIZATION". 54*^ 

worlds come and go. Suns are kindled and extinguished. 
Constellations spread the floor of heaven for a time, to be 
swept away by the aeonic march of events. In the pro- 
gress of eternity how many cycles of world-life have been 
spent; what vicissitudes has each molecule of matter 
experienced; how many stations has it occupied, how 
many functions performed. But we pause. This very 
witness of cosmic changes testifies to something perma- 
nent and changeless. The molecule has not changed. 
As hydrogen, as silica, as water, or other form of matter, 
it maintains its identity in all the worlds, in all the re- 
motest spaces of the realm of cosmic existence. It throbs 
in Sirius with the same signal as in Capella. Its vibra- 
tions are measured by the same infinitesimal in Orion and 
in the sun, and in the laboratory of the experimenter. 
The quartz molecule which forms the gravel of the garden 
walk is the same which slept for ages in the masses of Ar- 
chaean quartzite. When the quartzite came into existence, 
the molecule was ancient. It had taken part in the history 
of the molten ages of the planet; it had been part of the 
primordial fire mist in which the first lines of cosmic 
organization were traced. It grows into nothing else; it 
grew out of nothing else; it is primordial, completed and 
perfect. It was not, like everything else, compounded; it 
was not evolved; it does not disintegrate or become effete. 
The mutations which we have traced belong to the forms 
of matter. The molecule belongs to a different category 
of existence. If we conceive the molecule resolvable into 
atoms, then the conclusion remains of the atoms. Be- 
tween the changeful and the changeless is an infinite 
gulf. And with all their qualities of permanence and 
indestructibility and perfection and uniformity, the mole- 
cule has been multiplied by millions of millions of mil- 
lions — each molecule cast in the same mould, endued 
with the same form, animated by the same energies. 



548 THE COSMIC CYCLE. 

How has it been multiplied? In a universe organized 
through processes of evolution, what is the origin of a 
thing unevolved? In a world of effects and causes, what 
is the cause of a thing which had no antecedent ? Our 
thought here trembles on the primal verge of being. 
Beyond — is the abyss of nothingness; here — are the 
seeds of a universe. These are not grown in the nursery 
of the natural world. 

Finally, as just intimated, the future life of cosmical 
organization is as clearly set within limits as its past. 
There is an ultimate goal toward which all cosmical 
matter is tending. That goal is not the actual condition 
of our world, for we see here everything in a state of 
change; and the moon exemplifies an ulterior state. It 
cannot be the Lunar phase, for even there solar light and 
heat, and terrestrial influences, and universal gravitation, 
and meteoric matter, and a pervading ether, are all con- 
spiring to disturb the condition of absolute repose. The 
finality lies in the impenetrable darkness of the distant 
future. What it may be we can only conjecture; but one 
impending stage of all cosmical matter is positively writ- 
ten upon the face of the moon. Not only must our own 
planet reach finally that refrigerated and inhospitable con- 
dition, but the sun itself must ultimately fade to a dark- 
ened planet and become extinguished in the heavens. 

These thoughts summon into our immediate presence 
the measureless past and the measureless future of mate- 
rial history. They seem almost to open vistas through 
infinity, and to endow the human intellect with an exist- 
ence and a vision exempt from the limitations of time and 
space and finite causation, and lift it up toward a sublime 
apprehension of the Supreme Intelligence whose dwelling 
place is eternity. 



i 



PART IV. 

EVOLUTION OF COSMOGOKIC 
DOCTEINE. 



Les Savants sont de nos jours unanimes a admettre que notre systeme 
solaire est du a la condensation d'une nebuleuse qui etendait autrefois au-del^ 
des limites occupies actuellement par les planetes le plus lointaines * * * 
La th^orie * * * a ete bien confirme, et, pour ainsi dire, demontre par la 
ddcouverte des nebuleuses gazeuses.— Le Pere Secchi. 



PAET IV. 

EVOLUTION OF COSMOGONIC DOCTRINE. 

WHEN a great theory has grown into existence, and 
the general assent of competent judges has con- 
verted a sublime conception from the state of a provi- 
sional hypothesis to the position of a strengthening doc- 
trine, there is unusual interest in glancing over the pro- 
gress of science and noting the actual steps by which the 
guess became theory, and the theory, doctrine. I shall 
therefore supplement the subject of nebular cosmogony 
with a concise historical sketch. This I think will be ac- 
ceptable to the reader because cosmological science has 
now attained such a position that every intelligent person 
should possess some information respecting the exact 
views of Kant, Herschel and Laplace, the chief founders 
of this science as now accepted ; while no adequate sum- 
mary of their speculations — most especially those of 
Kant — is sufficiently accessible to the general reader. 

550 



CHAPTER I. 

PRE-KANTIAN SPECULATIONS. 

§ 1. GREEK PHILOSOPHERS. 

THE familiar phenomena of whirlwinds, whirlpools 
and eddies seem to have suggested to reflecting 
minds in all ages, the possibility of some vortical theory 
for the explanation of the mechanism of the world. The 
diurnal and annual motions of the heavenly bodies were 
early submitted to an attempt at solution based succes- 
sively upon Eudoxian, Hipparchian and Ptolemaic systems 
of cycles and epicycles. When the Copernican theory 
began to gain a foothold, it could no longer be doubted 
that the method of vortices was the method of the heav- 
ens. We now understand how the mutual actions of the 
numerous bodies in the material universe must result in a 
general and most intricate network of virtual revolutions 
about centres of gravity. 

The doctrine of the rotation of the earth about an axis 
was taught by the Pythagorean Hicetas, probably as 
early as 500 B.C. It was also taught by his pupil Ec- 
phantus, and by Heraclides, a pupil of Plato. The im- 
mobility of the sun and the orbital rotation of the earth 
were shown by Aristarchus of Samos as early as 281 B.C., 
to be suppositions accordant with facts of observation. 
The heliocentric theory was also taught, about 150 B.C., 
by Seleucus of Seleucia on the Tigris.* It is said also 
that Archimedes, in a work entitled Psani'mites, incul- 

* Compare Whewell: History of the Inductive Sciences, Am. ed. i, 259; 
Delambre : Astronomie Ancienne. 

551 



552 PRE-KAXTIAN SPECULATION'S. 

cated the heliocentric theory. The sphericity of the 
earth was distinctly taught by Aristotle, who appealed 
for proof to the figure of the earth's shadow on the moon 
in eclipses.* The same idea was defended by Pliny. | 
These views seem to have been lost from knowledge for 
more than a thousand years. In 1356, Sir John Maunde- 
ville in his remarkable book of travels distinctly and in- 
telligently revived the ancient idea. J In 1346, Nicolaus 
Cusanus wrote a work § in which the idea of the Greeks 
was scientifically defended. Thus was opened the way 
for Copernicus.il 

The introduction of the vortical conception into theo- 
ries of the origin of things dates from an antiquity equally 
high. According to Anaxagoras of Clazomenge, who was 
born about 500 B.C., the primitive condition of things 
was a heterogeneous commixture of substances which 
continued motionless and unorganized for an indefinite 
period. " Then the Mind began to work upon it, commu- 
nicating to it motion and order. ^ The Mind first effected 
a revolving motion at a single point ; but ever-increasing 
masses were gradually brought within the sphere of this 
motion, which is still incessantly extending farther and 
farther in the infinite realm of matter. As the first conse- 
quence of this revolving motion, the elementary contra- 
ries, fire and air, water and earth, were separated from 
each other. But a complete separation of dissimilar, 
and union of similar elements was far from being hereby 
attained, and it was necessary that within each of the 

* Aristotle: Be Ccdo, lib. ii. cap. xiv. 

t Pliny: Natural History ^n, 65. 

X ITie Voiage and Travaile of Sir John Mauncleville, Kt., from the ed. of 
1725. London, 1866. Chap, xvii, especially pp. 180-182. 

§ De Doda Ignorantia. 

' Aryabatta, an Indian astronomer, about 1322, A.D., and some of his coun' 
trymen, are said, however, to have taught the heliocentric doctrine. Draper : 
Intellectual Development of Europe. 145. 

^Aristotle : Fhysica, viii, 1. Also, Diog. Laertius: Lives. 



SPECULATION'S OF KEPLER. 553 

masses resulting from this first act, the same process 
should be repeated."* The views of Leucippus, and of 
Democritus, his disciple, promulgated about 430 B.C., 
present a closer relation to some aspects of the modern 
nebular theory. They maintained that space was eter- 
nally filled with atoms actuated by an eternal motion. 
The weight of the larger atoms forced them downward, 
while simultaneously the lighter ones were thrust upward. 
Mutual collisions produced lateral movements. Thus 
rotary motion was generated, " which extending farther 
and farther, occasioned the formation of worlds." f These 
views were extended by Epicurus and the Roman Lu- 
cretius,]; though by them the lateral motion of the atoms 
was ascribed to choice — a conception of the animated 
nature of atoms which has been revived again and again, 
and especially in the seventeenth century by Gassendi 
and Leibnitz, and in the nineteenth century by Rosmini, 
Campanella, Bruno and Maupertuis. 

§ 2. SPECULATIONS OF KEPLER. 

The celebrated Kepler, about 1595, devised a curious 
hypothesis which made use of a vortical movement within 
the solar system. The conception of attraction and repul- 
sion had come down from the epoch of Empedocles, by 
whom they were designated "love" and "hate;" but to 
the time of Kepler, no interaction between masses of mat- 
ter had been distinctly recognized which was generically 
different from magnetism. When, therefore, Kepler pro- 
jected a theory employing attraction and repulsion, he 
attributed these actions to cosmical magnetism. The sun 
was regarded by him as a great magnet revolving on an 

* Ueberweg: History of Philosophy ^ i, 66. 

t These views seem to have been quite definitely formulated by Leucippus, 

though they are generally attributed to Democritus. See Diogenes Laertius : Lives. 

X Similar theories were long afterward entertained by Torricelli and Galileo. 



554 PRE-KAJ^^TIAIT SPECULATION'S. 

axis whose position had been determined by the Divine 
Being.* The solar substance was immaterial, and sent 
forth radially an emanation of the same substance. 
These radiations rotated with the sun, and thus consti- 
tuted a vortex. The whole surface of the sun was re- 
garded as attractive, while the centre was repulsive. 
These two forces were everywhere in equilibrium, and 
hence a planet in any appointed position would be retained 
constantly at its mean distance, and would be carried 
around the sun in its vortex. The departure of the plane- 
tary paths from the circular form was explained by the 
supposition that each planet had one attractive side and 
one repulsive side^ and that these were turned alternately 
toward the sun. Thus when the attractive side was turned 
toward the sun, the planet approached a perihelion, and 
when the opposite side was thus turned, the planet retired 
to its aphelion. The deviation of the orbital plane from 
the equatorial plane of the sun was accounted for by the 
supposition that the planet was furnished with certain 
' fibres " which, acting like a rudder against the sea of 
solar emanations, guided the body above or below the 
plane of the solar equator. Kepler, perceiving that the 
motion of the central sun must in time be diminished and 
exhausted, provided for its constant restoration by the 
perpetual care of the Creator, or by the assistance of a 
spirit designated for that employment. 

A hypothesis more fanciful, and less in accord with the 
requirements of physical principles has not been offered in 
ancient or modern times. ^ 

§ 3. THE VORTICAL THEORY OF DESCARTES. 

By far the ablest expositor of a vortical conception of 
the universe, without ostensible appeal to universal attrac- 

*See Gregory: Elements of Astronomy, Sec. 10, Prop. 66; Delambre: As- 
tronomie du Moijen Age. ^ 



THE VORTICAL THEORY OF DESCARTES. 555 

tion, was Descartes.* He assumed, in brief, that infinite 
space is filled with infinite matter; that matter was origi- 
nally in a chaotic, formless condition; that the cosmical 
bodies arose at first from vortical motions in the original 
mass. These bodies float in the rotating matter like a sleep- 
ing traveller in a ship at sea. Gravitation was not recog- 
nized, and all physical phenomena w^ere explained by the 
laws of pressure and impulsion alone. 

More particular!}^, Descartes supposed that all matter 
was in the beginning divided by God into particles of 
nearly equal size. They were small and were actuated by 
motions about their own centres. Not being in absolute 
contact, the universal substance was of the nature of a 
fluid. Groups of particles rotated also, about other cen- 
tres remote from each other and thus established a corre- 
sponding number of vortices. Mutual friction reduced 
the particles to globules of various sizes, which he desig- 
nates "particles of the second element." The matter of the 
" first element " consisted of minute parts rubbed from 
the corners of the globules. This matter rotated with 
great rapidity. Its abundance was more than sufficient to 
fill the interstices between the globules, and the surplus 
was collected at the centre of the vortex, in consequence 
of the retirement of the globules by virtue of their circu- 
lar motion. The centrally accumulated fluid became a 
sun in the centre of each vortex. The sun had a rapid 
rotation about its axis, in common with the motion of the 
surrounding particles, and it also continually emitted 
some of its own substance which escaped radially with a 

* His views are set forth comprehensively in the work entitled Benati Des- 
cartes Principia Philosophim, Amsterdam, 1644. Many editions of the complete 
works and of single works of Descartes have been published in Latin, French 
and German. Perhaps the best is Qiiuvres de Descartes, nouvelle edition pre- 
cede d'une introduction par Jules Simon, Paris, 1868. A summary of Descar- 
tes' vortical theory may be found in David Gregory's Elements of Astronomy, 
Physical and Geometrical, 1701. See, also, in the Encyclopcedia Britannica, 
Art. Descartes. 



556 PEE-KAXTIAX SPECULATIOXS. 

spiral motion, through the narrow passages between the 
globules along the plane of the equator. These emana- 
tions, in their vortical movement carried the globules with 
them. But those nearest the centre moved with a higher 
velocity than those more remote, and must therefore have 
been smaller; for if of equal or greater mass, their greater 
momentum would have carried them off to the greater dis- 
tances instead of the less. What is ajBSrmed of any one 
vortex may be similarly affirmed of every vortex. But 
beyond a certain limit of distance from the centre, the 
globules are assumed to revolve with a quicker motion and 
to be of sizes as small as the lower ones. The orbit of 
Saturn marks this limit in the solar vortex. 

Descartes posited also a "third matter," produced from 
the original particles. As the "first matter," resulting 
from friction, settles through the interstices between the 
rapidly revolving globules it becomes "twisted and chan- 
nelled," and when it reaches the central orb it rests upon 
its surface like froth or foam, and constitutes spots, like 
those seen on the surface of the sun. In some cases, this 
foam dissolves into an ether surrounding the sun; but in 
others it accumulates in a thick and dense crust which 
weakens the expansive force of the central bod}^ 

Xow, if we /Suppose the central sun of any vortex to 
become so "covered with spots" as to be materially 
"weakened" it would be gradually overcome by the vorti- 
cal whirl of a neighboring sun. If now, this subjugated 
sun possess a feebler power of agitation, or have less 
solidity than the globules of the second element moving 
near the circumference of the subjugating vortex, but 
more than those nearer the centre of the vortex, then the 
subjugated sun will descend through the sujugating vortex 
until it arrives at a point where its solidity or aptitude to 
persevere in motion along a straight line, is equalled by 
that of the globules there surrounding it. In this situa- 



THE VORTICAL THEORY OF DESCARTES. 557 

tion it will float in equilibrium in the matter of the first 
element, and have no other motion than that which is im- 
parted by the motion of the fluid in which it rests. It 
would thus become a planet revolving in a fixed orbit. It 
follows that the original space in which our present solar 
vortex exists contained seventeen or more vortices, the 
central bodies of which by becoming weakened, were sub- 
dued successively by the predominating vortex of our sun, 
and approached or retired to the positions in which their 
forces were in equilibrium with those of the surrounding- 
globules. Some of these planetary centres, while yet they 
were suns, were of such mass that they exerted a more 
powerful influence than our sun, upon the vortices in their 
neighborhood; and thus certain minor vortices ranged 
themselves about Saturn, Jupiter and the earth, while all 
the others took at once, suitable positions in the solar vor- 
tex. Subsequently, the vortices of Saturn, Jupiter and 
the earth, yielding to the superior power of the sun, sank 
to their several places of equilibrium. The vortices became 
extinct, and the bodies moved as planets about the sun. 
The central bodies of still other vortices, if more than 
seventeen existed within the present solar vortex, passed 
away in right lines out of the solar vortex and became 
comets. 

It follows from this theory that the denser bodies of our 
system are those more remote from the sun. For a similar 
reason the moon turns constantly the same side toward the 
earth, because the opposite side possesses the greatest 
density. The planets rotate on their axes because they 
were once lucid stars, the centres of vortices. Even now, 
the matter of the first element, collected at their centres, 
continues its gyratory motion and acts on the planets. 

Finally, the centres of the planets must be subject to 
irregularities of the same meaning as those which charac- 
terize all natural things. All the bodies in the universe 



558 PRE-KAXTIAK SPECULATIOXS. 

are relatively contiguous to each other, and act upon each 
other. The motion of each is varied in innumerable ways. 
Hence, though all the planets approach a circular motion, 
in a common plane, none of them attain completely to 
these conditions. 

This fanciful, arbitrary and really indefensible, but most 
ino'enious theorv commanded a wonderful deo-ree of cred- 
ence and respect, and even contended, on the continent, with 
the Newtonian theory of universal gravitation for accept- 
ance as an adequate explanation of planetary phenomena. 

§ 4. THE THEOilY OF LEIBNITZ.* 

1. Sis Protogcea. — The daring conception of a primi- 
tive molten world was clearly formed by Leibnitz. When 
once this thought was entertained as even a speculative 
doctrine, it was easy to push beyond to the conception of 
a world heated to volatilization, and a whole system in a 
state of incandescent vapor, or at least of dissociated 
particles in some such condition as Descartes had postu- 
lated. The mental process by which Leibnitz advanced 
toward the full acceptance of the vortical planetary the- 
ory, appears from some passages in his Protogcea,\ which 
I here translate: 

"§ II. It pleases the wise hands of nature that the globe of the 
earth, like all created things, should exist in a regular form; for 
God does not make things without method; and whatever is pro- 
duced per se [by progress from earlier to later conditions. A. W.] 
either grows insensibly particle by particle,:}: or is fashioned byselec- 

*Le grand Leibaitz lui-meme s'amusa a faire, coiiime Descartes, de la 
terre im soleil eteint, im globe vitrifie, sur lequel les vapeurs, etaut retombe'es 
de son refroidissemeut, formerent des mers qui dc'poserent ensuite les terrains 
calcaires.— Ciivier: Discours sur les Revolutions de la Surface du Globe, 45, 
Paris, 1828. 

t Leibnitz: Protogcea, sive de prima facie Telluris, etc., first published 
entire in 1749. An abstract, however, was published in Acta Biuditorum^Leip- 
zig, 1683, to which later contributions wore continued till 1689. 

X Insensibiliter aut coticrescit per particulas. Here we have the "principle 
of continuity' applied to the changes of the material world. 



THE THEORY OF LEIBNITZ. 559 

tion and conflict of the parts in effecting tirrangements among them- 
selves.* Hence the asperity of the mountains which roughen tiie 
face of the earth supervened on a primitive condition. And assur- 
edly, if the earth could be conceived as liquid in the beginning, it 
should, of necebsity, be also symmetrical. But it agrees with the 
general laws of bodies that solid substances should consolidate from 
liquid. This is evidenced from solids found inclosed in solids, cer- 
tain layers and nuclei being very often rounded off at their- angles 
and limits, and veins being frequently observed in rocks, and gems 
in stones. But also numerous relics of ancient things everywhere 
exist — plants and animals, and things artistically fashioned into a 
novel and stony similitude. It follows that what we now recognize 
as hard is a later formation ; it must, therefore, have been originally 
fluid. Ultimately, fluidity itself results from internal motion, and, 
as it were, from some degree of heat.f This is shown by experi- 
ments. For even with undiminished heat, water becomes glass, 
while, on the contrary, corrosive fluids, strong through some hidden 
motion, are with difficulty congealed. But heat or internal motion 
is from fire or light; that is, a 'pervading subtile spirit. Thus, we 
arrive at the moving cause, whence, also, Sacred History derives the 
beginning of its cosmogony. 

§ III. As far, therefore, as human knowledge is able to reach, 
either by ratiocination or by the teaching and tradition of the Sacred 
Scriptures, the first step in the formation of things is the separation 
of light and darkness, that is of things active and things passive ; 
the second is, the discrimination of things passive among themselves, 
that is, the separation of things liquid from things dry ; which two 
are distinguished, among things passive, according to their different 
power of resistance and degree of firmness. Thus bodies are vari- 
ously transformed by fires and floods. Moreover, the things which 
we see opaque and dry were in the beginning ignited; then, after a 
time, being exhausted of their waters, the elements were separated, 
and, as we may believe, the present aspect of the world emerged. 
The facts according with these views certain priests of wisdom build 
into the form of a hypothesis, and explain more distinctly the 
method of separation. Namely, that certain vast globes of the uni- 
verse were brought into existence, which then either shone by their 

* Aut j)ro sese disponentium deleciu confliciuque tornatur. Here is a distinct 
statement of the principle of "natural selection." 

t Porro ipsa fluiditas ah intestino est motu; et lanquam gradii calorie. It is 
interesting to note here also a plain statement of the modern "mechanical 
theory of heat." 



560 PRE-KAIs^TIAN' SPECULATIOI^S. 

own light, according to the fashion of a fixed star or our own sun, 
or were projected from a sun of their own, their matter being subse- 
quently boiled out and spuinescent, and scoriae issuing forth through 
fusion — a condition of matter perhaps analogous to that in the 
spots which dim the light of our sun, and which the ancients some- 
times denied him, though they recognized a feeble obscuration, but 
which the optical instruments discovered in our age enable us to 
study. By excess, however, of accumulated material, the internal 
heat was overcome, and a cooled crust was formed surrounding the 
body. Thence came into existence the dark star, shining by reflected 
light, like the platiets. That we inhabit such a Vulcan they either 
suppose or pretend to be established by that Mosaic separation of 
light and darkness. It is, indeed, believed by most people, and is 
also intimated by the sacred writers, that a store-house of fire is 
established in the interior of the earth, which at some time will again 
burst forth. This conjecture is confirmed by the vestiges of the 
primitive aspect of nature which still remain. For every scoria from 
fusion is a kind of glass. But the crust ought to resemble scoria, 
for this covered the fused matter of the globe as in a furnace of 
metal, and became hardened after fusion. That such, indeed, is the 
surface of our globe (for it is not given us to penetrate further) we 
actually experience. For all earths and stones return to glass by the 
agency of fire, and so much the more as they approach nearer the 
nature of a rude rock. Neither, meanwhile, would I deny that 
earthy and vitreous products may possibly be born from waters 
through transformations of a higher order ; since it is evident that 
the waters are pregnant with various bodies, and that matter itself, 
everywhere similar to itself, is able per se to assume some certain 
form. ISTor are there any ultimate unchangeable elements. But it 
is sufficient for us in this place, that by human art, through the 
efficient agency of fire, earthy matters become converted into glass. 
The great bones of the earth themselves, those naked rocks and 
eternal flints, what, since everything passes very nearly into glass, 
are they, unless consolidated from bodies formerly fused by that 
great primitive force which flre has hitherto exerted over facile mat- 
ter? For this, surpassing by an enormous excess the power of our 
furnaces and their degree of duration, what wonder is it if it then 
produced results which men are unable to imitate, although art daily 
advances, and continually produces things new and unheard-of, yes, 
indeed, brings bodies fused by its own fire sometimes, to a high de- 
gree of hardness. When, therefore, all substances which are not 



THE THEORY OF LEIBNITZ. 561 

dissipated in vapors are at length fused, and, especially through .the 
power of burning lenses, assume the nature of glass, it is easy to 
understand that glass is, as it were, the basis of the earth; and that 
its nature lies concealed under the masks of very many other bodies, 
its particles being variously corroded and elaborated, partly by 
solution and agitation of waters, partly by repeated elevations in 
vapor and distillations, until finally by the aid of salts added to the 
power of heat, stony hardness is reduced to mud suited for nourish- 
ing plants and animals, and is even reduced also, to a volatile nature. 
Meantime, by as much as anything in the earth is more nude and 
primitive, and approximated to the simple constitution of rocks, 
this the more persists in the fire, though it is fused by the highest 
heat, and finally vitrifies. For even a calcareous rock which resists 
our furnaces is reduced to glass by the speculum. Even as to sand, 
which is a large, and at the same time the simplest portion of the 
earth, and fills immense deserts and shores, and the bottom of the 
sea, and underlays the better soil with gravel, to what can it be re- 
ferred on examination, more properly than to stones or translucent 
fluors, and, as it were, glass, by motion either in a state of fusion 
or by other means, reduced to small fragments ? — a result also easily 
produced by fire if salts are present, and these have never been 
wanting from the beginning. 

§ IV. From this genesis of things comes the origin of the salt 
sea observed to-day. For as things burned out attract moisture 
after cooling, whence oils are produced by chemists by means of lixi- 
viation, so it appears, in the beginning of things, while our globe 
was yet incandescent and the opaque was not yet separated from the 
light, moisture, being expelled by fire, was not present in the atmos- 
phere; but subsequently reproduced by a true process of distillation, 
it was again condensed into watery vapors through abatement of the 
heat; and when, by the cooling of the terrestrial surface, the mass 
became absorbed, it was finally returned in water, which bathing the 
face of the earth — the wide remains of the recent burning — re- 
ceived fixed salt in itself. Hence originated a sort of lixivium 
which flowed together in the sea. Indeed, from the analysis of 
plants, as has been noted from the observations of the Parisian Aca- 
demicians, we have learned that two fixed salts remain in lixivia — 
the one alkaline, as the artisans express it, the name being derived 
from a plant which our people call soda, and the Arabes calu the 
other marine, and more inclined to acid. Lastly, it may be sup- 
posed that the crust, contracting through cooling, as among metals 
36 



562 PRE-KAXTIAX SPECULATIOXS. 

and other substances which by fusion become more porous, left bub- 
bles, great according to the magnitude of the thing, that is, cavities 
under vast arches, inclosed in which was air or humor ; that then 
also certain matters separated in layers, and that through variation 
of material and of temperature, masses subsided unequally, so that on 
every hand, disruptions occurred, the fragments being tilted in 
valley slopes, while the solider parts, like columns, held the highest 
place. Thus, therefore, mountains came into existence. The weight 
of the waters was added for preparing a basin in the still soft bottom. 
At length, either through weight of material or force of elastic 
vapors, the immense arches were broken ; the humor in the cavities 
being expelled through the ruins or flowing spontaneously from the 
mountains, inundations followed, which thus again deposited sedi- 
ments by intervals ; and these hardening, and presently a similar 
cause returning, diverse strata were laid down one upon another, 
and so the face of the orb as yet tender, was many times renewed. 
At length, these causes becoming quiet and equilibrated, a more per- 
sistent state of things emerged. Whence now, a duplex origin of 
solid bodies is intelligible — one when they solidify from fusiofi by 
fire, the other when they consolidate from solution in water. It is 
not therefore to be supposed that stones arise from fusion alone. 
That this is most possible from the first mass and basis of the earth, 
I admit. Xor do I doubt that afterward, when liquid matter flowed 
over the surface of the earth, after the return of quiet, a great vol- 
ume of materials was deposited from the eroded rubbish, of which 
some formed various kinds of earth, others hardened into rocks. 
Among these, diversified strata in regular order of superposition tes- 
tify to the various recurrences and intervals of precipitation. 

§Y. These things may perhaps be said without dissent con- 
cerning the cradle of our orb; and they contain the germs of a new 
science which might be designated Natural Geography ; we venture, 
however, rather to suggest it than to construct it. For, although 
the sacred monuments of the divine oracles favor, we nevertheless 
defer judgment to those with whom is the right 6i interpretation. 
And although the vestiges of the ancient world are united in the 
present aspect of things, nevertheless, posterity will define every- 
thing more correctly, when the curiosity of mortals shall have pro- 
ceeded so far as to describe the kinds of soil and the rocky strata 
extending through wide regions. But indeed, I do not impute all 
inequalities of the earth or the nature of the sea bottom to primitive 
solidification. It suffices to have deduced by geueral causes, 



THE THEORY OF LEIBN^ITZ. 563 

the skeleton itself, and, as it were, the bones of the earth's exte- 
rior, and the sum of its entire structure. For these seem to be the 
true sources, if you seek them, whence the immense cavity of the 
ocean has been derived, and the monstrous masses of the mountains, 
as for instance, * * * j^^^ j ^\Q i^q^ thus deny that the globe, 
being now solid, minor conflagrations and motions of the earth, and 
limited inundations,* and sedimentations from standing waters, 
have supervened, which have often taken possession of extensive 
tracts and transformed them; for of these the vestiges which still 
remain with us will presently be described. Nor is it doubtful that 
straits have been cut by incursions of the sea; that lands have been 
absorbed in the abyss or transfoi-med into morasses; that shores 
have now been inundated, now uncovered ; that lower places have 
been depressed, and narrows shut up by the ruins of mountains and 
the obstruction of the courses of the waters ; that by turns lakes burst- 
ing through outlets violently opened, have excavated valleys for 
their discharge; that volcanic mountains have been opened and 
closed ; that pumices have been spread far and wide, and the marks 
of conflagrations indelibly impressed. But what ought to be in- 
ferred from causes acting on a larger or smaller scale, posterity will 
sometime more easily determine, after the home of the human 
species shall have been more thoroughly explored." f 

We find here very definitely enunciated, the germs of 
modern geological theory. A few of Leibnitz' contempo- 
raries, more especially Steno, had already expressed a 
rudimentary conception of the agency of the sea in the 
deposition of fossil remains; but Leibnitz was the first to 
suggest the full extent of igneous action, and thus fur- 
nished the basis for the famous Plutonic theory which 
divided opinion a century later. More conservative, how- 
ever, than the Plutonists, he united, as modern geology 
does, the principle of aqueous action with that of igneous 
action; and deserves to be counted one of the most philo- 
sophic and far-seeing among the founders of the science. 

*Priuatas eluuiones. 

+ Most of the remainder of the Protogaea i(? devoted to accounts of caverns, 
metallic ores, gems and other minerals, with quite extended descriptions of fos- 
sil remains, the whole accompanied by eleven very good copperplates of illus- 
traiions. 



564 PRE-KAXTIAX SPECULATIONS. 

Let us glance now more particularly at his cosmogonic 
views, which, so far as his own thought is concerned, were 
the logical outcome of his geology. 

2. His Plaaetogeny. — The Cartesian theory com- 
manded the general approval of Leibnitz; and his opin- 
ions were published as early as 1680,* in an essay on the 
causes of the celestial motions. He assumes that every 
body immersed in a fluid and moving in a curved line 
must be acted upon by the fluid itself. For a body mov- 
ing in a curve tends continually to take the direction of a 
tangent, and would do so if there were nothing to restrain 
it. But nothing can restrain it unless contiguous to it; 
and in a fluid there is nothing contiguous except the fluid 
itself. It follows, therefore, that the fluid must possess 
the same motion as the body. This reasoning applies to 
the planets. 

As the j)lanets revolve about the sun according to the 
law of equal areas, the "ether or fluid orb of each planet*' 
must move according to the same law. This will be the 
case if we conceive the fluid to consist of an infinitude of 
concentric circles, each revolving with a velocity inversely 
proportional to its distance from the sun. A circulation 
of this kind is termed harmonic. The actual motion of a 
planet is something more than this, since it moves with 
unequal velocity and at a varying distance from the sun. 
It must, therefore, be actuated also by a paracentric force, 
oy virtue of which it approaches and recedes from the 
sun. But, in approaching the sun, its velocity is acceler- 
ated because then immersed in a fluid having a more rapid 
vortical movement, and in receding from the sun its 
velocity must be retarded until it accords with that of the 
zone of the fluid to which it has attained. ''Consequently, 
the harmonic proportion holds not only in arcs of circles, 
but in describing any other curve," since the minute arc 

*Acta ErmlUorum, Leipzig, 1680. 



THE THEORY OF LEIBNITZ. 565 

described in each infinitesimal element of time is essen- 
tially identical, whatever the form of the curve. 

The paracentric motion is composed of two factors; 
one is the tangential tendency w^hich the planet must 
experience even when swimming in and with a fluid; the 
other is the sun's attraction, or rather the planet's gravity.* 
Since we know that each planet revolves in an ellipse with 
the sun in one focus, and with a velocity according to 
the law of equal areas; and since no law of circulation 
but the harmonic will afford the necessary conditions for 
this, it follows that we must seek a law of gravity, which, 
combined with the tangential tendency, will constitute 
such paracentric motion as in connection with the har- 
monic will carry the planet along the perimeter of an 
ellipse. f This law he demonstrates and enunciates as 
follows: "If a heavy body be carried in an edipse, or 
any other conic section, with a harmonic circulation, and 
the centre, both of attraction and circulation, be in the 
focus of the ellipse, then the attractions or solicitations of 
gravity will be as the squares of the circulations directly, 
or as the squares of the radii or distances from the focus 
reciprocally." This, it will be observed, is precisely the 
law of gravitation previously announced by Newton and 
noticed in the Acta Eruditorura at Leipzig. 

Leibnitz confesses that he is not prepared to indicate 
what motion of the ether it is which imparts that tendency 
Called gravitation,]; nor what causes the relation of differ- 
ent planets expressed by saying that the squares of their 

* Such an expression is employed at the same time that Leibnitz opposes 
the Newtonian theory. This tendency here called attraction is (perhaps disin- 
genuously) ascribed to some impulse received from the ambient fluid, as from a 
magnet. 

tSome later Cartesians, as John Bernouilli, conceived a way of producing 
elliptic motion in a circular vortex. 

X The successors of Leibnitz and Descartes thought they had discovered 
a means of constructing a vortex so as to produce a tendency of bodies to the 
centre. 



566 PRE-KAKTIAX SPECULATIOXS. 

periodic times are as the cubes of their mean distances 
from the sun. 

One of the most obvious, as also most fatal, of the 
objections to these vortical theories, is the fact that in 
spite of the power of the fluid to carry the masses of the 
planets in a uniform direction, the tenuous comets pass 
through it unhindered and undeflected, and in all imagin- 
able directions, and travel at the same time, like the 
planets, with velocities regulated by the law of equal 
areas. * 

§ 5. THE VORTICAL THEORY OP SWEDENBORG. 

In 1733-4, Emanuel Swedenborg, a Swedish philoso- 
pher^ during a sojourn abroad, published a remarkable 
work on the Principles of Things, in which a vortical 
theory was set forth which in many respects was original 
and seems to be less amenable to certain objections than 
the theories of his predecessors, f The exposition of 

*The reader may find these theories discussed in Gregory's Astro no?nice 
Mementa [or Elements of Astronomy, Physical and Geometrical, 1701]. Objec- 
tions to the admission of an interplanetary fluid are extensively urged by Cotes 
in his Preface to Newton's Prlncipia. On the conflict between Cartesianism 
and the Newtonian philosophy, sea Whewell: History of the Inductive Sciences, 
Am. ed., i, 429-32. 

t Emanuel Swedenborg: Principia Rerum Nafuraliu7n. Dresden and Leip- 
zig, 1733-4, 3 vols, folio. [First Principles of Natural Things, being new at- 
tempts toward a Philosophical Explanation of the Elementary World.] This 
was produced in elegant style, with copious engravings, at tiie expense of the 
Duke of Brunswick. I have not seen the original work, nor is a translation of 
it included among the translations published by the "American Swedenborg 
Printing and Publishing Co.," New York, 1875; but through the kindness of Mr. 
T. F. Wright, one of the editors of the Neiv Jerusalem Magazine, of Boston, I 
have been favored with the loan of a translation of the first volume, made by 
Rev. Augustus Clissold, M. A., and published in London, in 1846. As Sweden- 
borg is principally known as a mystical writer on religious and theological sub- 
jects, it has been customary to pass by his scientific speculations as not having 
been based on any just and adequate apprehension of physical principles. 
Whether the charge be merited or not, we are interested in knowing what his 
views were. Moreover, Swedenborg did not retire from public and professional 
life to enter upon his course of theological meditation and study, until at the age 
of 57, which was eleven years after the publication of his Principia. Dunng 
his professional career he was ranked as one of the most eminent scientists of 



THE VORTICAL THEORY OF SWEDENBORG. 5G7 

his theory is prolix and abstruse in an eminent degree ; 
and a casual reader not possessed of a suitable cast of 
mind would pronounce it full of paradoxes and contradic- 
tions. Assuming^ however, that the author must have 
possessed a logical apprehension of the things of which 
he wrote, I have educed and condensed the essence of his 
theory in the following statement. 

The first cause is the infinite or unlimited. This gives 
existence to the first finite or limited. That which pro- 
duces a limit is analogous to motion. The limit produced 
is a point, the essence of which is motion ; but being 
without parts, this essence is not actual motion but only 
a conatus to it. From this first proceed extension, space, 
figure and succession or time. As in geometry a point 
generates a line, a line a surface, and a surface a solid, so 
here the conatus of the point tends toward lines, surfaces 
and solids. In other words, the universe is contained hi 
ovo in the first natural point. 

The motion toward which the conatus tends is circular, 
since the circle is the most perfect of all figures, and 
tendency to motion, impressed by the Infinite, must be 
tendency to the most perfect figure. "The most perfect 
figure of the motion above described must be the per- 
petually circular ; that is to say, it must proceed from 
the centre to the periphery and from the periphery to 
the centre. * * * jl^ must necessarily be of a spiral 
figure, which is the most perfect of all figures. In the 
spiral there is nothing but what partakes of a certain 

Sweden, and of Europe, enjoying the society and patronage of the first officials, 
and of the princes and rnlers of several conntries?. Especially was he known as 
a mathematician and mechanician. He wrote also on astronomy, physics, min- 
eralogy and monetary science. He was offered the chair of pure mathematics 
in the University of Upsal, hut declined; was a corresponding member of the 
Academy of Sciences of St. Petersburg, and one of the earliest members of the 
Royal Academy at Stockholm, where his portrait hangs near that of Linnseus, as 
one of the past presidents of the Academy. 
*Clissold's translation, i, 63. 



568 PRE-KAXTIAX SPECULATIONS. 

kind of circular form ; and nothing within it is put into 
motion but what takes a circular direction. The motion 
proceeds perpetually to a circle. The spiral motion may 
be said to be infinitely circular ; every motion around the 
centre is a circle ; its progression toward the periphery 
is circular [curvilinear ?] ; in a word, its figure is circular 
[curvilinear?] in all its dimensions and bearings. Per- 
petual circulation is the same as a perpetual spiral ; hence 
the most perfect figure of motion, as well in conatus as 
in act, can be conceived to be no other than the perpetual 
spiral, winding, as it were, from the centre to the peri- 
phery, and again from the periphery to the centre ; thus 
it is a perpetual reciprocation and spiral fluxion." * 

But all this conatus and possibility of motion exists as 
yet only in a metaphysical sense. There is no actual 
motion. " Before anything can be produced, conatus 
must pass into act ; like what is formal into what is real ; 
and, consequently, the point must pass with its conatus 
into motion." f Motion, however, is the only medium by 
which anything new can be produced. Motion, itself, 
which is merely a quality and a mode, and nothing sub- 
stantial, may yet exhibit something substantial, or the re- 
semblance of what is so, provided there be anything sub- 
stantial put into motion." t Now, if an infinitely small par- 
ticle be set in infinitely rapid motion by a spiral, it may be 
made to generate a line, a surface, or a solid, by suitable 
species of motion ; and thus a "simple finite or first sub- 
stantial" would be originated. As tlie simple finite de- 
rives its existence from the motion in ^the primitive 
conatus, it will have an actual spiral motion. Thus the 
potential becomes actual. The simple finite is an epitome 

* Op. cit. 63-4. Compare also, p. 82, speaking of flnites. 1 leave it for others 
to explain the legitimacy of confounding circles and spirals. 

■fOp.cit.,e(i. 

* Op. at., 68. 



THE VORTICAL THEORY OF SWEDENBORG. 569 

of the world.* It fills space, but is minute beyond con- 
ception. It is endowed with figure. All its characters 
are exactly repeated in other finites. Possessing the same 
active force as the point, "it is able to finite and produce 
the subsequent and more compounded finites." f Thus 
compounds arise. 

The motion in the finite is spiral and reciprocal, like 
that conative in the point. This spiral motion determines 
the position of two poles, and these assume the form of 
cones. With poles are coordinated " an equator, ecliptic 
meridians and other perpendicular circles." | The finite, 
from its inherited conatus, develops " a progressive motion 
of all the parts and spires." Moreover, since the centre 
of the spiral is not coincident with the centre of gravity 
of the corpuscle, the latter is rotated and constrains the 
corpuscle to a local motion. " Therefore, not only all the 
primitive force in the point, but that also which is derived 
into its sequents consists in this: that the motion, state or 
conatus in a point tends to a spiral figure. This motion, 
state and conatus cause an axial, and at the same time, a 
progressive motion. These together produce another or 

* This account of the origin of a substantial particle seems to proceed on 
the principle of the infinitesimal calculus. Granted the infinitesimal matter, 
masses of matter are the necessary derivative. The infinitesimal finite seems 
to be assumed for a starting point in order to get as near as possible to a concep- 
tion congeneric with that of the original point, which is only conatus. But be- 
tween an atom of real matter and the absolute negation of matter in the point, 
is a chasm which does not seem to be bridged. Boscovich, who wrote in 1756 
{Tlieoria pliilosophioi naturalis redacta ad unicam legem virium in natura exis- 
tentium), escaped this difficulty by assuming that the atom was not extended, 
though possessed of mass — a mere centre surrounded by spheres of repulsion 
and attraction. Sir William Thomson has propounded also, a dynamical theory 
of atoms (On Vortex Aloms, Proc. Roy. Soc. Edinboro', 18 Feb., 1867) in which 
the "vortex ring'' of Helmholtz is made the type of an atomic ring formed of 
a i)rimitive fluid perfectly incognizable except in this vortical mode of motion. 
The analogy of this to the vortical "first finite" of Swedenborg is apparent, 
though an important difference exists in the use of a primitive fluid by Sir W. 
Thomson. 

t Op. cit., 79. 

+ Op. cU., 86. 



570 pre-kaxttain^ speculations. 

a local motion, a motion in which consists the active 
power of finiting and compounding the sequents, and of 
modifjdng them throughout a lengthened series in the 
manner in which we perceive by our senses, the world at 
large to be modified." * 

The world and the solar s^^stem are conceived as evolved 
through the continuance and enlargement of the processes 
mentioned above as in their incipiency. It would be too 
tedious for the reader to be conducted through the several 
hundred pages in which the author discourses of " second 
finites" and "third" and "fourth finites," "actives" 
and " substantials." Suffice it to say that the solar 
space is a grand vortex; f that it has grown through the 
concurrence of similar vortices; that no other force has 
been needed than the one at the solar centre, while this 
proceeded from the primitive point; J that the sun is 
stated to rotate on an axis; "that the solar matter con- 
centrated itself into a belt, zone or ring at the equator or 
rather ecliptic; that by attenuation of the ring it became 
disrupted; that upon the disruption, part of the matter 
collected into globes, and part subsided into the sun, form- 
ing solar spots; that the globes of solar matter were pro- 
jected into space; that consequently they described a 
spiral orbit; that in proportion as the igneous matter thus 
projected receded from the sun, it gradually experienced 
refrigeration and consequent condensation; that hence fol- 
owed the formation of the elements of ether, air, aqueous 
vapor, etc., until the planets finally reached their present 
orbits;" § that the process of system building extended to 
the stars, and that the Milky Way is the axis of the 
firmamental vortex. 

* Op. cit., 91-2. 

tSee. especially, Part III, ch. iv. Be chao universali soils et planetarum, 
deque separatione ejus in planetas et satellites. 
X Op. cit., 203-8. 
§ Rev. A Clissold's Introduction, p Ixxxi. 



THE VORTICAL THEORY OF SWEDENBORG. 571 

It will thus be seen that Swedenborg's theory begins 
with an immaterial point, like the monad of Leibnitz; 
that it therefore has no inertia to be overcome, but is 
gifted with an inherent force which finally flows out into 
actual motion and actual substance. Kepler also regarded 
the vortical medium as the immaterial emanation from the 
sun's body, but the planets which swam in it were mate- 
rial and were floated as in a material medium. According 
to Swedenborg, the planetary body is not passive, but 
possesses an inherent conatus to motion. It is difficult to 
perceive why Leibnitz, who posited self-moving monads, 
did not, like Swedenborg, avail himself of this mode of 
energy, and thus escape the difficulties imposed by the 
motion of inert bodies, and the presence of a medium 
which, by some mysterious selection, bore the planets in 
its vortex without affecting the comets. 

The Swedenborgian theory is not regarded as com- 
pletely set forth in the Principia. His later works are 
thought to be "fuller of philosophy." Mr. Wright, of the 
Neva Jencsalem 3fagazine, Boston, has pointed out pas- 
sages which he thinks afford additional light.* 

* These are Divine Love and Wisdom, beginning at No. 282, and The True 
Christian Religion, Nos. 76 and 78, especially No. 78. I take the liberty of 
quoting from a letter of Mr. Wright, what he regards as the deeper significance 
of these passages. "You will there notice that the idea is that creation is by 
the self-subsisting God; that His infinite love and wisdom demanded the uni- 
vers-e; that its production was not by extension of the infinite, nor by the ex- 
tension of nothing, but by the determination of the infinite into recipient 
forms produced by itself by degrees, ench of which was the medium of creative 
energy to that next below; that this process terminated in matter; that this 
gradation was, is and always will be the vehicle of transmission of life from the 
Divine; that the preservation exemplifies the creation; that the production of 
forms of life on earth was through the production of their si)iritnal prototypes, 
when the time came for it in the process of development; thug, tliat the evolu- 
tion was subject, at every point, lo the creative process. This seems to us to be 
the whole view, of which that in the Principia is only a part." (Letter of Febru- 
ary 24, 1880.) 



572 PRE-KAXTIAiq^ SPECULATIO]!^S. 

§ 6. THE SPECULATIOXS OF THOMAS WRIGHT. 

The next prominent writer who put forth cosmogonic 
views worthy of comparison with later nebular theories 
was Thomas Wright, of Durham.* Unable personally to 
consult his writings, I am indebted to Kant for an intima- 
tion of the nature of Wright's sjDeculations. In the Intro- 
duction to his General History of Neiture^ he sa3^s: "The 
First Part is chiefly occupied with a new system of world 
structure. Herr Wright, of Durham, whose treatise 1 
first became acquainted with through the Hamburg' schen 
freien Urtheilen of the year 1751, gave me the first sug- 
gestion toward the contemplation of the fixed stars, not 
as a promiscuous assemblage without visible order, but as 
a system which sustains the greatest resemblance to a 
planetary system, so that, just as in the latter the planets 
are confined very nearly to a common plane, so also, the 
fixed stars arrange themselves as nearly as possible in their 
successive zones, upon a definite plane which must be re- 
garded as extended through the whole heaven, and, by 
means of their densest aggregation in such plane, trace 
out that luminous belt known as the Milky Way."f 

It appears that Wright entertained the conception of 
other firmamental systems, as well as of higher orders of 
systems successively ascending until the entire universe 
"revolved about the throne of God," as we have some- 
times found the thought expressed in English literature. 
Kant refers to Wright again in connection with the ques- 
tion of the central body of the universe.]; "What may 
be the constitution of this fundamental piece of the entire 

* Thomas Wright: An Original Theory, or Neiv Hypothesis of the Universe, 
London, 1750, 4to. An American edition, with Notes by Prof. C. S. Rafinesque, 
was published in 8vo at Philadelphia in 1837. No cop}^ exists, however, in the 
library of the Academy of Natural Sciences at Philadelphia : nor have I been able 
to obtain a copy of the work in any edition. 

t Kant's SammtUche Werke, i, 220. 

X^siaf^ Sdmmtliche Werke, i, 311. 



SPECULATIONS OF THOMAS WRIGHT. 573 

creation, and what may be found upon it, we leave it to 
Herr Wright, of Durham, to determine. He, with fanati- 
cal enthusiasm, elevated in this happy spot, as on a throne 
of universal nature, a powerful being of the divine sort, 
possessed of spiritual attractive and repulsive powers, who 
draws to himself all virtues and repels all vices in the 
boundless sphere through which his activity spreads." 

These are not weighty items for Kant to place on the 
credit side of his account with Wright; and it would ap- 
pear that nebular theory is still less indebted than Kant to 
the bold English speculator. 



CHAPTEE II. 
KANT'S GENERAL HISTORY OF NATURE. 

No Other thinker of modern times has been throughout his work so pene- 
trated with the fundamental conceptions of physical science ; no other has been 
able to hold with such firmness the balance between empirical and speculative 
ideas.— Prof. R. Adamson. 

IMMANUEL KANT is the author who is generally re- 
garded the first to outline the modern cosmogonic 
theory on a well apprehended basis of physical principles. 
The treatise* in which his views are set forth is, in many 
respects, remarkable. As it is known only in a general, 
and imperfect, way, to a large majority even of the well 
informed, I shall offer a somewhat extended digest of its 
positions. It will be noticed that, in accordance with the 
spirit and usages of his age, he entered quite freely upon 
themes which a strict judgment would set down as at best 
only collateral. But I shall endeavor to fairly reproduce 
the spirit of these parts, as well as those which are more 
strictly scientific. I am the better pleased to do this be- 
cause Kant is not generally credited with entertaining 
some of the beliefs which are clearly reflected in the theo- 
logical passages of this work. 

§ 1. FIRMAMENTAL ORGANIZATION. 

The author first directs attention to the familiar phe- 
nomena of the Milky Way. The diffused light of that 

*Kant: Allgemeine Naturgeschichte iind Theorie des Himmels^oder Versuch 
von der Verfassung mid dem mechanischen Ursprunge des ganzen Weltgebdudes, 
nach Newton'' schen Gnindsdtzen abgehandelt. Konigsberg u. Leipzig, 1755. 
Kant's Sdmmtliche Werke, Hartenstein edition, Leipzig, 1867, Bd. i, SS. 307-345. 

574 



FIRMA MENTAL 0KGAN1ZATI0:N^. 575 

belt he attributes, like Herscliel after him, to the multi- 
tude of stars which lie in the line of vision; and the 
definiteness of the belt of light he compares to the "zo- 
diac" within which tlie planets of our solar system move. 
All these stars he conceives to be travelling in orbits about 
the centre of the starry system, near which our sun is 
placed, or, perhaps, around more than one centre. These 
motions secure the stability of the system, and endow it 
with endless perpetuity. He regards the comets as origi- 
nal members of the solar system, and their high inclina- 
tions and erratic movements are compared with tlie more 
scattered fixed stars which lie more or less removed from 
the zone of the Milky Way. Such stars he calls "the 
comets among the suns." But why are not these move- 
ments among the stars observed by astronomers? He 
replies, w^th characteristic sagacity, that their immense 
distances render their changes of position imperceptible 
within a lifetime, and calculates that four thousand years 
would be required for one of the nearest to move over an 
arc of one degree. But he anticipates that the time will 
come when these movements will be discovered.* He 
remarks that the ancients noted stars in definite positions 
from which they have disappeared, and conjectures that 
they have simply changed their places. The excellence 
of instruments and the perfection of science give hope of 
fixing this conjecture on a certain basis. De la Hire had 
already remarked decided change in the stars of the 
Pleiades. 

In the next place he directs attention to remarkable 
patches of light now known as nebulas. Huygens had 
regarded them as openings in the firmament through 
which the glow of heaven shone. Maupertuis had consid- 

* This anticipation has been f iiltilled, but the stellar movements do not 
present that consentaneousness required by Kant's theor3\ They move in all 
directions, and not alone iu paths parallel with the plane of the Mi3ky Way. 
(See pp. 140-1.) 



576 

ered them heavenly bodies of vast dimensions. But Kant 
ventured to regard them as remote firmaments of stars 
whose immense distances reduced their light to a faint 
blended luminosity. To him they were only other Milky 
Ways, with motions and world systems akin to those pre- 
sented by our firmament and solar system. 

He dwells on these conceptions with warmth, and says: 
" They open to us an outlook upon the limitless field of 
creation, and afford an exhibition of the work of God, 
which is commensurate with the eternity of the divine 
Worker." * * * '*The wisdom, the goodness, the 
power which here reveal themselves are infinite, and in 
the same measure productive and unresting; the plan of 
their revelation must, therefore, be precisely like them, 
infinite and boundless."* 

The great philosopher falls into the error of regarding 
the comets as members of the solar system, and as gener- 
ated by the same mechanical cause. He thinks a transi- 
tion may be discovered between the planets and comets. 
The eccentricities of the planetary orbits increase, as a 
rule, from the nearer to Saturn — the remotest known in 
the time of Kant. The exceptions offered by Mercury and 
Mars may be attributed, he says, to their smaller mass, by 
which they received an excess of the centrifugal influence. 
Is it too much, then, to anticipate that planets which we 
may expect to discover beyond Saturn will possess a still 
higher eccentricity, and thus exhibit a graduation toward 
the class of cometary bodies? If this is likely, then not 
alone will there be revealed a transition tpward comets in 
an increasing eccentricity of orbit, and thus a proof that 
the cause which imparted to both their orbital motions 
became, with increase of distance, feebler and less able to 
maintain the equilibrium of centripetal and centrifugal 
motions, but also less able to restrict the remoter bodies 



*Sammtliche Werke, 243. 



i 



PLAifETOGENY. 577 

to the common ecliptic plane ^vhich the comets have been 
permitted so singularly to abandon. We may, therefore, 
expect the discovery of planets beyond Saturn, whose 
eccentricity will diminish the gap which now exists be- 
tween planets and comets, and which will be visible only 
in perihelion, a circumstance which, with their smaller 
dimensions and feebler light, has hitherto prevented their 
discovery. The last planet and the first comet may be 
regarded the same, and its eccentricity, we may believe, 
is so great that in its perihelion it intersects the orbit of 
the next interior planet which, perhaps, is Saturn itself. 

§ 2. PLANETOGENY. 

In the second part of this essay Kant approaches, first, 
the question of planetary origins and the causes of their 
motions. In contemplating the harmonious movements of 
the planets, two considerations impress us: First, so 
extended a system of mutual conformities seems to dem- 
onstrate a common cause. Second, the interplanetary 
spaces are so vast and so vacant that the admission of 
interacting influences seems impossible. Newton, says 
he, for this reason, could not admit the existence of any 
material cause acting across the intervals of the planet- 
ary framework, to impress common movements. He 
affirmed that the immediate hand of God had established 
the observed order without the intervention of the forces 
of nature. There must, however, be some conception 
which shall unite these two conflicting principles in a true 
system. The interplanetary spaces must have been for- 
merly filled with a supply of efficient material for impress- 
ing the uniform motions of the heavenly bodies; and after 
gravitation had cleared those spaces, and all disseminated 
material had been gathered in separate masses, the plan- 
ets must continue to move in unresisting space with the 
motion impressed upon them, I assume, he says, that all 
37 



578 kais"t's gexeral history of mature. 

the matter of the solar system, in the beginning of all 
things, existed dissolved into its elements, and filled the 
entire space of the system. Its existence is an outcome 
from the eternal idea of the Divine Mind. It was en- 
dowed with a tendency to form, through natural develop- 
ment, a more perfect constitution. But the difference in 
the kinds of elements induced motion in nature, and an 
organization of the fittest* out of chaos; so that the 
stagnation which must have resulted from universal iden- 
tity of material was disturbed, and the chaos began to be 
organized at the points of the more powerfully attracting 
particles. These drew to themselves lighter particles, and 
the larger masses attracted the smaller, until at length a 
collection of bodies remained, animated by motions inher- 
ited from the past conditions. 

But nature has other forces in store. The force of 
repulsion tends to the dissolution of matter. This force, 
during the process of descent of particles toward the cen- 
tre of attraction, developed at times a transverse action, 
which deviated the particle from a direct line, and inau- 
gurated a tendency to rotary motion. Thus came into ex- 
istence the planetary and also the solar motions, f The 
beginning of planetary formation, however, is not to be 
sought alone in Newtonian gravitation. This would be 
too slow and feeble. We should rather say that the first 
organization took place through the accumulation of sim- 
ple elements united by the customary laws of cohesion, 
until such masses were formed that the Newtonian attrac- 
tion became sufficient to continually enlarge them by 
action from a distance. J; 

Turning next to the densities of the planets, and the 

* " Das Vornehinste." 

t Our present knowledge of the invariability of the total quantity of motion 
within a system exposes a fallacy in this reasoning. 

iThis is another m'sappreheusion, since gravity acts upon particles as well 
as masses. 



PLANETOGENY. 579 

relations of their masses, it is apparent, he says, that the 
condensation of the original matter must be proportioned 
to the distance of the particles from the attractive centre. 
Newton had believed that the variations in density were 
produced by the direct will of God. The lightest portions 
of the earth, for instance, must be distributed over the 
surface. Why then is the density of the sun less than 
that of the planets ? Because the planets near the centre, 
and in fact all the planets, are composed of particles which, 
from their superior density have been drawn toward the 
centre, displacing the lighter particles or mingling with 
them in more than the normal proportion, while on the 
contrary, the body at the centre is composed of the gen- 
eral average of particles in respect to density, among 
which the lighter constitute the greater part.* In accord- 
ance with this view, concludes the author, '' the moon is 
twice as dense as the earth, and the latter four times as 
dense as the sun ; and the earth, according to all calcula- 
tion, will be surpassed in density by the interior planets 
Venus and Mercury." f The increasing ratio of planetary 
masses as we recede from the sun is connected with the 
increasing diameters of the spheres of attraction of the 
planets, as their distances diminish severally the sun's in- 
fluence. The excessive tenuity of the original stuff is 
shown by the fact that if all the planets were reduced to 
the density of our atmosphere, their matter would fill 

*The passa2e {Op. cif., p. 256) is involved and ob?care. It is strange that 
the author did not perceive that the process of increasing condensation in the 
dffused mass could not be arrested at any given distance from the centre, but 
must be continued quite to the centre, and thus render the central body the 
densest of all. 

+ Modern astronomy has determined the following densities for these bodies : 
Sun, .255; Mercury, 1.21 (which is according to prediction); Venus, 1 03; Earth, 
1.00; Moon, .607. Nevertheless, the remarkable coincidence remained, as 
pointed out by Buflfon, that the mean density of all the planets is to the density 
of the sun as 640 to 650. But finallj', the mean density of all the planets, accord- 
ing to present knowledge, and allowing for diflferences in the planetary masses, 
is to the density of the sun as 296 to 255 or as 640 to 552. 



580 kaxt's gexeral history of xature. 

fourteen hundred thousand times the space of the earth; 
while this is thirty million times less than the entire space 
which the matter of the planets is supposed to have filled 
originally. 

The gradually increasing eccentricity of the remoter 
planets is produced by the diminished centripetal force of 
the solar mass upon the descending particles, and their 
lower density and hence feebler power to overcome the 
resistance offered by the heavier jDarticles to their direct 
descent toward the sun. These conditions attain their 
maximum in the region of the comets beyond the orbit of 
Saturn. To them are due also the high inclinations of the 
cometary orbits. As to the retrograde motions of certain 
comets, since they are in conflict with the theory, it is 
conjectured that with many of them the phenomenon may 
be only an optical illusion. 

Satellites have come into existence through the opera- 
tion, on a smaller scale, of the tendencies recognized in 
the organization of the planets. Axial rotations have 
been established by the primitive motions of the gathering 
particles. The synchronism of the moon's axial and 
orbital motions is a problem left for future solution.* The 
moon's rotation was probably more rapid once than at 
present. The same may be said of the rotation of the 
earth. The inclinations of the planetary axes may have 
been produced b}^ an excess of momentum of particles de- 
scending upon one hemisphere; but more probably, pertur- 
bations have intervened to disturb the original positions 
of the axes. Moreover, the uplift of mountain masses 
unsymmetrically disposed must tend to change the posi- 
tion and inclination of the axis of a planet, f though this 

*This seems a singular statement, since the author had already, in 1754, in a 
prize essay presented to the Academy of Sciences in Berlin, ascribed this syn- 
chronism to tidal action exerted by the earth. 

tThis is substantially the problem discussed by Rev. Samuel Haughton 
{Froc. Boy. Soc.^ March 8, 1877, xxA^i, 51-5, 55-63; December 20, 1877, xxvi, 534- 



PLANETOGENT. 581 

change is confined within limits. Such orographic dis- 
turbances belong to the earlier periods of planetary life, 
and Jupiter seems to be actually undergoing changes inci- 
dent to the half -fluid and unsettled condition. " In such 
a state the surface can experience no repose. Upheavals 
and ruin reign upon it. The telescope itself assures us 
of this. The condition of this planet is perpetually 
changing." 

The author next considers the origin of the rings of 
Saturn. A planet lying at the distance of Saturn must 
have many agreements with the neighboring comets, if, in 
fact, it has entered the planetary class as assumed, through 
the diminution of its eccentricity. Viewing the planet 
thus, there was a time when its great eccentricity brought 
it, in perihelion, into close proximity with the sun. The 
intense solar heat lifted its lighter material from the sur- 
face in the form of vapor. At a later period, with a 
moderated temperature, the vapors assumed the form of 
tails, and at length the cometary aflinities of the planet 
were retained only in the permanent ring which surrounds 
it. In short, "Saturn has had a rotation upon its axis, 
and nothing more than this is necessary." * * * "I 
venture to declare that in all nature few things can be re- 
duced to an origin so intelligible."* The velocity of rota- 
tion of the ring calculated from the periodic time of a 
satellite, gives the velocity of the equatorial portion of the 
planet at the time of the separation of the ring. Thus 
the planet's rotation is found to be 6 h. 23 m. 53 sec, and 
he leaves it for the future to test the result, f 

Kant had knowledge of only a single ring around Sat- 
urn. But he calculated that tlie friction of outer and 

46). See, also, G. H.Darwin's criticism {Proc. Roy. Soc, March 14, 1878), and 
Prof. Haughton's reply {Ih., May 23, 1878^. 

* Op. clt., 275. Here is a distinct enunciation of the principle of annulation 
afterward employed by Laplace. 

tit is given in recent works as 10 h. 14 m. 



582 ka^j^t's gek^eral history of nature. 

inner parts, due to dijfference of velocity must tend to the 
destruction of the ring. Instead of this event, however, 
it would separate into several concentric rings, each re- 
volving in its own period,* The number of these rings 
could be computed if the degree of connection between 
the constituent particles were known. In any event, the 
equilibrium and stability of the rings is provided for. As 
to the condition of the matter of the rings, Kant continu- 
ally speaks of particles and small parts [Theilchen), and 
clearly conveys the identical conception which has been 
enunciated by Peirce and Clerk-Maxwell in recent times. 
In a note of later date, he cites with satisfaction a record 
made by Cassini f half a century before, in which the con- 
jecture is offered that "perhaps this ring may be a svmrin 
of small satellites, which to an observer from Saturn may 
present somewhat the aspect of the Milky Way from the 
earth." Kant also cites with satisfaction the confirmation 
already furnished by Cassini, of his argument for the ex- 
istence of several rmgs. He takes great pleasure, he says, 
in offering his theory of the rings, since he has the hope 
that it may be confirmed by new observations to be made 
with the improved telescope which he hears that Bradley 
has had placed at his disposal. 

As to the possibility of rings about other planets, he 
shows by a simple calculation, based on the diameter of 
Jupiter, its period of rotation and the attractive force 
upon its surface, that a Jovian ring is impossible under 
present relations of these factors. He shows the same 
in reference to the earth.]; But in former times, when the 

* Compare the alleged tendency to stratification, stated on p. 119. 

iMemoires Acad. Sci., Paris, 1705. 

$In an editorial note is given the substance of an oral statement made by 
Kant concerning his theory in 1791. He thinks it has received much confirma- 
tion, especially through the light thrown upon it by a " Supplement " published 
by Herr Hofrath Lichtenberg, who suggests that in any aeriform '-Urstoff'' 
disseminated through space a high degree of elasticity must subsist, until 
through gravitational pressure it should be destroyed ; after which the density 



THE COSMOS IJT ITS TOTALITY. 583 

axial rotation of the earth was much more rapid, a ring 
may have existed. "What beauty of aspect for those who 
were created to inhabit the earth as a Paradise ! How 
great a convenience for those on whom nature smiled from 
every side ! " This ring must have consisted of watery 
vapor. Why may not its disruption through contact with 
a misdirected comet, or the process of cooling and. con- 
densation, have precipitated upon the earth that destruc- 
tive flood, the Mosaic narrative of which has so puzzled all 
commentators ? * 

In this connection the Zodiacal Light is conjecturally 
referred to the same explanation as the Saturnian ring. 
It is regarded as a ring of particles surrounding the sun,! 
and lying nearly in the plane of his equator. 

§ 8. THE COSMOS IN ITS TOTALITY. 

The author proceeds now, in the seventh chapter of 
the Second Part, to a more particular consideration of the 
infinitude of the creation at large, both in respect to space 
and time. " The cosmical fabric, through its immeasur- 
able magnitude and the endless variety and beauty which 
shine forth from it on all sides, impresses us with silent 
amazement." This feeling is enhanced by the discovery 
that this vast array"of phenomena flows from the orderly 
and eternal working of a single general law. The stars 
are centres of other systems like our own. They are com- 
posed of the same elementary particles. Like the planets 
of our zodiac, they are arranged in a limited zone which 
we style the Milky Way. " The Milky Way is the zodiac 

would become so increased that great heat would be developed which, in the 
larger bodies like the sun, would be arcompanied by luminosity, but in the 
smaller, like the planets, would produce only an internal heat. Here is the con- 
tractional theory in the bud. 

* This recalls William Whiston's grave conjecture that the Flood was caused 
by a blow from the tail of a comet, 

t Poetically styled the "Halsschmuck der Sonne." This is precisely the 
modem view. 



584 KANT'S GEi^ERAL HISTORY OF NATURE. 

of the higher world orders." But even beyond the 
bounds of the system of the Milky Way, are other 
firmamental systems — other Milky Ways. We contem- 
plate with amazement their faint figures pictured on the 
concave vault of heaven. The worlds of all these sys- 
tems, to insure their stability, must necessarily possess 
motions analogous to those of our own system.* But has 
the succession of ever ascending world systems no end ? 
It would be preposterous to contemplate the minute por- 
tion of space which we survey as the limit of the field of 
the divine activities. It is more suitable, more necessary 
to conceive the realm of the material creation as abso- 
lutely without bounds. We have good ground to con- 
clude that the store of created matter \ suffices for the 
production of a chain of cosmical order without limit. 
The basis matter itself is an immediate consequence of 
the divine existence, and must necessarily be so exhaust- 
less and enduring as to extend the development of material 
organization over a plan of creation embracing all exis- 
tence possible, without measure and without end. One 
might well conceive an endless succession of mutually 
disconnected world systems ; but such a plan would not 
provide for the perpetuity of order ; and unless the 
common princij^le of attraction extended through the en- 
tire universe of matter, there would be wanting that char- 
acter of persistence which is the mark of the choice of 
God. J But a universal co5rdinating principle implies one 
common centre, and one vast central mass of matter. 
Here the process of creation began. From this middle 
point it has extended continually outward over the infi- 
nite chaotic waste of unorganized material atoms. I 

*Iu this connection he uses the expression, Dm Liclit luelches nur eine 
eingedrilckte Bewegicng ist, which is equivalent to the intimation that light is 
only " a mode of motion." 

t Der Vorrath des erschafenen Naturstoffes. 

X Die Bestotidigkeit die das Merkmnl der Wold Gottes ist. 



THE COSMOS 11^ ITS TOTALITY. 585 

know of nothing which can lift the soul of man to a 
nobler amazement than the outlook over this boundless 
field of Almighty power. Worlds rise into being upon 
worlds, in endless progress ; and beyond the outer bounds 
of the widest realm of order, confusion and chaos forever 
contend on a field as limitless as if the work of creation 
had not already attained an endless development. Assign 
what diameter we will to the completed creation, we are 
always near the middle point ; beyond the periphery of 
the sphere, over the infinite expanse, lie buried in the 
stillness of night, the germs of order awaiting the pro- 
gress of eternity to be quickened into active life. So the 
process of cosmical organization extends itself. " Crea- 
tion is not the work of a moment." Millions and moun- 
tain ranges of millions of ages will flow away and "the 
creation will never be complete. It was indeed once be- 
gun, but it will never end." 

It is perhaps a daring conjecture that the cosmic pro- 
ductiveness of one part of immensity implies the com- 
parative exhaustion of another part. But the resources 
of the universe are never diminished, for they are nothing 
else than the exercise of the divine omnipotence itself. 
The decay of worlds is but a part of the universal order 
which brings plants and animals and man himself to de- 
struction, only to be succeeded by new organisms at some 
other point. " Whatever has origin and beginning has in 
itself the characteristic of its finite nature ; it must decay 
and come to an end." As man in course of time, retires 
from the stage on which he has acted his part, so worlds 
and systems, when their role is played, vanish from the 
scene. The infinitude of creation is wide enough to spare 
a world or a Milky Way as easily as a flower or an insect. 
"Meanwhile eternity is adorned with ever varying mani- 
festations, because God remains active in the unceasing 
work of creation." 



586 KAis^T's GEjq^ERAL HISTORY OF :n^ATURE. 

But when a system of worlds has fallen into disorder 
and decay, will no power be extended to effect a reorgan- 
ization ? We cannot long remain in doubt when we 
reflect that the ceaseless exhaustion of the motions of the 
planetary system must finally precipitate planets and 
comets together upon the body of the sun, and that then 
the solar heat must undergo an increase so immeasurable 
as to dissipate again the particles of the common mass 
through the distant regions of space from which they had 
been originally gathered together. Then must begin 
again the process of world organization whose completed 
cycle has been traced. 

As a planetary system seems destined to decay, so the 
hosts of the system of the Milky Way must be conceived 
as wasting inevitably the forces by which they are ani- 
mated. Countless suns will be precipitated upon the 
mighty central mass; but the tremendous shock will kindle 
an unimaginable intensity of glow, which must dissolve 
the bonds of matter, and expel its ultimate constituents 
again throughout the vast limits before engirt with the 
fiery girdle of the firmament. The soul of man in think- 
ing of events of such stupendous magnitude sinks within 
him in deepest amazement. But the vastness of objects 
and events so enstamped with the characters of change 
and mutability leaves the soul still unsatisfied; "it feels a 
desire to know more intimately that Being whose intelli- 
gence, whose greatness, is the fountain of that light which, 
as if from a central source, illuminates the totality of 
nature." "Happy soul if amid the tumult of the elements 
and the ruin of nature, it can look down always from its 
lofty position, and see the current of desolation which 
brings ruin to all finite things sweep by, as it were, be- 
neath its feet." "When, then, the fetters which hold us 
bound to the vanity of created existence, in the moment 
appointed for the transformation of our being shall have 



OUR SUN" AND OTHER SUNS. 587 

fallen off, then will the undying spirit, freed from depend- 
ence on finite things, find the enjoyment of true happi- 
ness in communion with the eternal existence." 

§ 4. OUR SUN AND OTHER SUNS. 

The more particular constitution and activities of the 
sun result from the nature of the primitive particles and 
their mode of condensation. The lightest parts of the com- 
mon matter which moves in the interplanetary spaces, from 
lack of adequate momentum are overcome by centripetal 
force and precipitated on the central body. But these 
parts are also the most energetic in the production of fire; 
and thus we see that through their addition to the central 
body it becomes a flaming orb. " On the contrary, the 
heavier and ineflicient material, and the lack of fire-pro- 
ducing particles make of the planets only cold and dead 
clumps deprived of such a property." The sun must be 
surrounded by an atmosphere. " Without atmosphere no 
fire burns." Now, considering the great mass of the sun, 
to what a density must this atmosphere attain, and what 
intensity of combustion must it support. In this atmos- 
phere ascend clouds of smoke consisting of commingled 
grosser and finer particles which, cooled in the higher 
regions, precipitate a rain of pitch and sulphur which 
afford the flames new aliment. This atmosphere, too, like 
that of the earth, is beaten by winds, and we may well 
imagine to what violence they must attain. But as is 
manifest, all flame devours its atmosphere, and without 
doubt the solar atmosphere must undergo a slow exhaus- 
tion. It is true, the interactions of the elements tend to 
replenish the atmosphere, that vast supplies must, for a 
long time, burst forth from concealed caverns in the solar 
structure, and that many substances, like saltpetre, are 
exceedingly productive of elastic gases, yet, though such 
causes must greatly prolong the solar heat, it must be 



588 kakt's general history of kature. 

admitted the sun is in real danger of final extinction. The 
central body of our system will be quenched in eternal 
darkness. Undoubtedly, in the progress of decay, new- 
found material may sustain an occasional outburst of fiery 
energy, as with other suns in our firmament, which have 
been seen to assume a sudden luminosity and then to wane, 
yet our central orb must finally attain the exhausted and 
defunct condition which awaits all finite organizations. 
But its dead substance disseminated through space will 
plant chaos with the germs of new worlds. 

"Let us contemplate in imagination, from a nearer 
standpoint, an object so extraordinary as a burning sun. 
At a glance we behold oceans of fire which raise their 
flames to heaven; raging storms of most fearful intensity 
which rolling over the shores submerge at times the 
elevated regions of the orb, and at times sink back upon 
their borders; burned-out rocks which from their flaming 
throats project their frightful tongues of fire, and whose 
submergence and emergence by the fluctuating fiery ele- 
ments is the cause of the appearance and disappearance of 
the solar spots; dense vapors which choke the fire, and 
which, uplifted by the force of the wind, condense in dark 
clouds which storm down again in torrents of fiery rain, 
and as burning streams descending from the heights of the 
solid land, pour themselves into the flaming valleys, the 
crash of the elements, the refuse of burned-out matter and 
the disintegration of exhausted nature which through this 
terrible stage of desolation itself works out the beauty of 
the world and the uses of the created being. '^ * 

If all the stars are flaming suns, still more must the 

* Op. cit., 309-10, In connection with the supposed " solid land " of the 
sun, the author observes, in a note, that the formation of a world from material 
In a fluid state necessitates the development of inequalities of surface. After a 
crust begins to form, the confined gases would uplift it in places and accumulate 
in immense caverns, producing on the surface alternating elevations and 
vallej s. This is an echo of Leibnitz. 



THE MECHANICAL CONSTITUTION OF THE WORLD. 589 

central body of the Milky Way be such. Why then does 
it not become visible? The answer is obvious, when 
we consider that if that body were ten thousand times 
the bulk of our sun, and removed a hundred times as far 
as Sirius, it would appear no larger than that star. 
Future times may discover it, or at least the region in 
which it is located. I venture the conjecture that Sirius 
himself is the central body of the Milky Way. What 
may be the nature and condition of the central mass of 
the universe is a problem which, perhaps, involves us in 
rasher conjecture than a scientific theory allows; but I 
cannot admit with Wright that here the person of the 
Godhead is specially present. The divine presence is 
essentially and equally in every domain and place. I im- 
agine, on the contrary, that the higher ranks of rational 
beings belong in regions remote from the universal centre. 
The density of the more central matter, whatever rela- 
tions subsist between matter and spirit, must necessarily 
impart a greater degree of sluggishness and dulness to 
more central intelligences, while a keener insight and 
deeper penetration should characterize spiritual life con- 
nected with the lighter matter which pervades the region 
of more freshly organized cosmical existence. 

§ 5. THE jMECHANICAL CONSTITUTION OF THE WORLD. 

The eighth chapter of the Second Part of the work 
offers some general reflections on the mechanical constitu- 
tion of the world, and the inferences which may be legiti- 
mately deduced. "It is impossible," the author says, "to 
contemplate the fabric of the world without recognizing 
the admirable order of its arrangement, and the certain 
manifestation of the hand of God in the perfection of its 
correlations. Reason, when once it has considered and 
admired so much beauty and so much perfection, feels a 
just indignation at the dauntless folly which dares ascribe 



590 kaxt's general history of nature. 

all this to chance and a happy accident. It must be that 
the highest wisdom conceived the plan, and infinite power 
carried it into execution." He proceeds to defend the 
mechanical theory of the universe against the charge of 
"naturalism/' and maintains that "the procedure of those 
naturalists who have delivered themselves of that kind of 
world wisdom must make solemn apologies at the bar of 
religion." One of the characteristic passages from this 
discussion is the following conclusion: "Nature, its gen- 
eral properties aside, is productive only of beautiful and 
perfect fruits, which display not alone harmony and per- 
fection, but also harmonize perfectly with the whole com- 
pass of nature, with the needs of man and the honor of 
the divine attributes. It hence follows that nature's prop- 
erties can possess no independent necessity, but that they 
must have their origin in a single Understanding as the 
ground and source of all being, in which they have been 
ordained in accordance with universal relations. All 
things which set forth reciprocal harmonies in nature 
must be bound together in a single existence on which 
they collectively depend. Thus there exists a Being of 
all beings, an infinite Understanding and a self-existent 
Wisdom, from which nature, in the whole aggregate of 
her correlations, derives existence. Further, it is not 
allowable to maintain that the activity of nature is preju- 
dicial to the existence of a highest Being; the more per- 
fect it is in its developments^ the better its general laws 
contribute to order and harmony, the more conclusive is 
the demonstration of the Godhead from wliom these rela- 
tions are borrowed. His productiveness is no longer the 
operation of chance, or the consequence of accident; from 
him flow^s everything according to unalterable laws, which, 
therefore, must produce only what is fit, because they are 
only the reflection of a scheme infinitely wise, from ^vhich 
all disorder is banished. It is not the fortuitous con- 



DEDUCTIONS TOUCHING HABITABILITY, ETC. 591 

course of the atoms of Lucretius which has builded the 
world; implanted forces and laws whose source is the 
wisest Understanding, have been the unvarying cause of 
that order which can only flow from them, not by chance 
but by ordination."* 

The author repeats the enumeration of the mechanical 
relations of the solar system, and maintains at length the 
improbability and unreasonableness of the view which 
ascribes them all to the immediate hand of God. Never- 
theless, he says: "We rightly believe that fit arrange- 
ments, which tend toward a useful end, must have a wise 
understanding for their originator; and we are perfectly 
at liberty to think, if we choose, that since the natures of 
things recognize no other origin, their present and uni- 
versal constitution must have a natural tendency to fit 
and mutually harmonious consequences." We need not 
hesitate to admit the operation of mechanical causes in 
nature, "since whatever proceeds from them is not the 
working of blind fate or irrational necessity, but is 
grounded finally in the highest wisdom, from which the 
constitution of nature borrows all its harmonies. This 
conclusion is perfectly correct: If in the constitution of 
the world order and beauty appear, then a Deity exists. 
But the other decision has not less foundation: If this 
order has proceeded from the general laws of nature, then 
all nature is necessarily a working of the highest wisdom. "f 

§ 6. DEDUCTIONS TOUCHING HABITABILITY AND UNITY 
IN THE SYSTEM OF WORLDS. 

The Third Part of the treatise is devoted to a research 
concerning the influence which must be exerted on the 
spiritual natures of the different planetary inhabitants by 
the nature of the matter of which their bodies must be 
constituted. An unquestionable and intimate interaction 

* Op. cit., 315-6. t Oih cii., 327. 



592 KANT'S GEi^ERAL HISTORY OF J?^ATURE. 

exists between mind and body. The original constitution 
and the casual conditions of the body control, to a large 
extent, the operations of the spiritual faculties. Since, 
therefore, the planets near the sun are composed of heavier 
and more sluggish matter than the remoter planets, it must 
be that their inhabitants are endowed with less mental 
agility and a feebler power for thought and imagination. 
Jupiter seems indeed to exist in that formative condition 
which naturally precedes the reception of organic popula- 
tions, but if his habitability is supposable, it seems strongly 
probable that his rational occupants, as well as lower ani- 
mals and plants are formed of such light and active ma- 
terial elements as give an easier and more rapid activity to 
the discharge of their organic functions. The same may, 
with still greater probability, be conjectured of Saturn. 
As the mind is correlated to the body, the rational natures 
of these distant populations must exceed our own corre- 
spondingly, in expertness and comprehension. As all our 
apprehensions of external things are measured by the im- 
pression made by the universe upon the susceptibility of 
our material faculties of cognition, it may well be imagined 
that the remoter populations of our system have attained 
to knowledge which stretches hopelessly beyond the reach 
of terrestrial intelligences. 

All material existence, however, is bound together in 
the common rational unity which finds its origin in the 
infinite Mind; and since even terrestrial intelligence is 
gifted with the power to seize hold on the chain of inter- 
connection, it discovers, though perhaps faintly, the reve- 
lations of the divine perfections which nature displays to 
all rational beings. Man, perhaps, stands, in the ranks of 
created beings, between those who, on the one hand, are 
too pure to sin, and those, on the other, who are too un- 
intelligent to sin. Man, perhaps, partakes exceptionally 
of the power to feel simultaneously the temptation to sin 



SYNOPSIS OF POINTS IN THE THEORY OF KANT. 593 

and the aspiration to purity; but he feels that his immor- 
tal soul, gifted with being which even death cannot end, 
but can only change, is destined to an eternity of life un- 
confined to a single planet, but privileged to seek and at- 
tain the loftiest knowledge revealed in all the departments 
of the domain of Omniscience. This remarkable treatise 
concludes with the following paragraph: 

"When, indeed, one's soul has been filled with contemplations 
like these, the view of the starry heavens on a cloudless night, con- 
fers a species of delight which only a noble susceptibility can appre- 
ciate. In the general stillness of nature and composure of thought, 
the mysterious intuitions of the undying spirit speak an unutterable 
language, and yield unformulated conceptions which it feels, indeed, 
but can never describe. If among the thinking creatures of this 
planet, beings exist so degraded that in the presence of all the in- 
ducements with which our exalted position invites them, they still 
hold themselves fast bound in the service of vanity, how ill-starred 
is this globe that it could nourish creatures so wretched! But how 
fortunate is it, on the other hand, that among all the most desirable 
conditions possible, a way is opened to attain bliss and exaltation 
which rise infinitely above all the preeminence conferred by the most 
advantageous organization of nature upon any one of the heavenly 
bodies." 

§ 7. SYNOPSIS OF POINTS IN THE COSMOGONIC THEORY 
OF KANT. 

1. Points correctly taken, according to more recent 
opinion. 

(1.) The diffused galactic light results from the multi- 
tude of stars lying in the direction of the galaxy. 

(2i) The stars must all be in motion, but their great 
distances demand thousands of years to render their mo- 
tions clearly apparent. Future observation will demon- 
strate these motions. 

(3.) The nebulae are other firmaments. Though this 
opinion was entertained by the elder Herschel respecting 
resolvable nebulae, recent opinion can hardly be said to be 
38 



594 ka^^t's gexekal history of xature. 

formed concerning them; but of irresolvable nebula? it de- 
nies the conclusion of Kant. 

(4.) The interplanetary spaces must have been filled 
formerly with a supply of matter. All the matter of our 
system was formerly dissolved, and filled the entire space. 
Its tenuity was excessive. 

(5.) Aggregation and organization began around cer- 
tain centres of attraction. 

(6.) The densities of the planets should diminish from 
the centre outward. 

(7.) The greater masses of the exterior j^lanets depend 
on the diminished power of the solar attraction in the 
remoter parts of the primitive stuff. 

(8.) The synchronistic motions of the moon are due to 
ancient geal tides on that satellite. The solar and lunar 
tides are correspondingly diminishing the earth's rotary 
velocity. 

(9.) The axial inclinations of the planets are probably 
due to perturbations. 

(10.) The uplift of mountain axes must affect the posi- 
tion of the axis of rotation of a planet. 

(11.) Jupiter exists in a half fluid and formative con- 
dition, not yet fitted for habitation. 

(12.) The ring-condition results from axial rotation of 
incoherent matter. 

(13.) Unequal velocities of outer and inner zones of 
a nebulous ring would result in separation into two or 
more rings. The ring of Saturn is probably multiple. 

(14.) The Sat^irnian ring is a swarm of discrete par- 
ticles or minute satellites. 

(15.) Jupiter and the earth do not present, in our 
day, the physical conditions required for the existence 
of rings. 

(16.) At a former period, when the rotation Avas much 
more rapid, the earth may have had a ring of watery vapor. 



SYNOPSIS OF POINTS IN THE THEORY OF KANT. 595 

(17.) The zodiacal light is a ring of particles surround- 
ing the sun. 

(18.) The fixed stars are centres of other systems com- 
posed of the same substances as our sun. 

(19.) Light is only a motion impressed. 

(20.) The process of world making is continuous. The 
decay of worlds is but part of the universal order which 
returns in new worlds. 

(21.) Whatever begins is finite and must come to an 
end. 

(22.) Planets and comets must finally be precipitated 
upon the body of the sun ; and the impact must generate 
enormous heat. 

(23.) Similarly, the present order which pervades the 
starry system must come to an end. 

(24.) The heat of the sun is destined to extinction. 

(25.) Extremely violent actions are taking place upon 
the solar surface, and the solar flames rise to heaven. 

(26.) The inhabitants of all worlds are bound together 
by a common rational apprehension of the system of 
nature. 

2. Points considered incorrectly taken. 

(1.) The fixed stars all move in orbits about a common 
centre. 

(2.) The comets are original members of the solar 
system. 

(3.) The eccentricities of the planetary orbits will be 
found to increase from the centre to the periphery of the 
system. 

(4.) Rotary motions resulted from repulsive action ex- 
erted from centres of matter on descending particles. 

(5.) The incipiency of aggregation resulted from co- 
hesions rather than from Newtonian attraction. 

(6.) The ring of Saturn results from intense solar heat 
exerted during perihelion, at a period when Saturn's ec- 



596 kaxt's gexeral history of xature. 

centricity was very great. It is a transformed cometary 
tail. 

(7.) Tiie precipitation of planets and comets upon the 
sun would create sufficient heat to dissipate the matter of 
the system and reinaugurate the process of planetary 
evolution. 

(8.) Mountainous inequalities in the crust of a solidi- 
fying world would result from the action of confined 
gases. 

(9.) There must be a central body for the revolutions of 
the Milky AY ay ; and this probably is Sirius. 



CHAPTEE III. 
DR. LAMBERT AND SIR WILLIAM HERSCHEL. 

§ 1. LAMBERT'S COSMOLOGICAL LETTERS.* 

LAMBERT'S work was written in popular style, and 
^ for several years excited much attention, both on 
the continent and in Great Britain. But he followed 
quite closely in the tracks of Wright and Kant. Though 
his style was popular, he claimed, like Kant, to found his 
conjectures on substantial scientific data. His motor 
principle was universal attraction. Finding within our 
planetary system residual phenomena, especially as made 
known by Lalande in the systems of Jupiter and Saturn, 
which could not be referred to causes within the system, 
he concluded that they must be attributable to influences 
exerted from without. Unlike Kant, he regarded the 
comets as strangers, or at best but naturalized sojourn- 
ers in the solar system. They constitute the material 
proof of the extension of the laws of attraction into the 
domain of the fixed stars. He felt, therefore, fully con- 
firmed in an opinion which he had long entertained, "that 
our planetary system is only the system of satellites of 
another celestial body."f Accordingly, as each of the 

* .Tohann Heinrich Lambert : Kosmologische Bnefe fiber die Einrichtung 
des Weltbaus, Augsburg, 1761, 8vo. Part of these letters were translated by the 
author as Lettres Cosmologigues and published in the Journal Helveligue de 
N-iuchatel, 1763-4; an extract also, by Merian under the title, Systlme du Monde, 
Bouillon, 1770, 8vo; also complete translation by d'Arquier, Amsterdam, 180f, 
Svo. A portion, also, as Cosmological Lelters, London, 1828. The substance of 
Dr. Lambert's speculations is given by Prof. S. Newcomb: Poptilar Astronomy^ 
465. 

t Letter to Bockman, Correspondance, annee 1773. 

.597 



598 DE. LAMBERT AXD SIR WILLIAM HERSCHEL. 

planets is, or may be, the centre of a system of re- 
volving orbs, and the sun is the centre of the plane- 
tary system, so the planetary system with other similar 
systems, must revolve about some centre sufficiently 
massive to control its motions. Each star in the heav- 
ens is the sun of a planetary system ; and in the clus- 
ters and constellations we see associated suns revolv- 
ing probably with a common motion about their common 
centres. This vast assemblage of solar systems consti- 
tutes a system of a still higher order, which we know 
as the Milky Way, or Firmament. Still beyond this are 
other great systems or galaxies in endless succession, in- 
visible to us only in consequence of their immense dis- 
tances. The central masses, unlike Kant, he conceived 
to be dark and solid bodies, rendered invisible by their 
opacity. 

This condensed statement indicates that Kant ap- 
proached much more nearly than Lambert to the modern 
conception of a nebular theory of the planetary system.* 

§ 2. SIR WILLIAM HERSCHEL'S RESEARCHES.! 

1. The Structure of the Heavens. — Sir William Her- 
schel found himself, through his own extraordinary inge- 
nuity and energy, in possession of telescopes of power 
unparalleled in previous times. His attention was accord- 
ingly directed chiefly to the nature of the fixed stars and 

* Johami Elert Bode, in an Introduction to Stellar Astronomy, entitled An- 
leitung zur Kentaiss des gestirnten H'unnitls, Hamburg, circa 1767, reproduced 
the conceptions then current from the writings of Kant -and Lambert. Many 
editions of this work have appeared — the seventh at Berlin. 1800. 

t These researches are contained in the Philosophical Transactions of the 
Royal Society of London, from 1T83 to 1818: but especially for the years 1784, 
1785, 1791, 1795, 1811 and 1814. A digest of this work is given by Arago : Analyse 
des Travaux de Sir William Herschel, m Annuaire du Bureau des Longitudes; 
and a brief account is contained in Xewcomb's Popular Astronomy, 465-74 and 
495. Compare, also. Sir John F. ^y. Herschel: Observations of Nebxdoi and 
Clusters of Stars, Made at Slough with a Twenty -feet Reflector, between the Years 
18S5 and 1833. Philosophical Transactions, Nov. 21, 1833. Prof. Holden's "Life" 
of Sir William Herschel I have not seen. 



SIR WILLIAM HERSCHEL'S RESEARCHES. 599 

the constitution of the stellar and nebular system. In 
1784* he announced that the sun must be included in the 
great stratum of the Milky Way. He explained his 
method of gauging the depths of the firmament, based on 
the assumption that the stars are somewhat uniformly 
distributed through space. On such an assumption the 
number of stars exhibited within the field of his. tele- 
scope would be an indication of the depth of the firma- 
ment in the direction of the line of sight. He concluded, 
as Kant had already done, that the greatest dimension of 
the firmament is in the direction of the Milky Way. Our 
firmament may be regarded as a flattened spheroidal 
assemblage of stars, having our sun near the centre, but 
not entirely symmetrical in its contour. In the direction 
of the galaxy the depth of the firmament, with the conse- 
quent number of stars lying in the line of sight, renders 
many of the individual stars undistinguishable, and pro- 
duces that cloud-like diffused luminosity characteristic of 
the galactic belt. On the sides, however, the diffused 
light is wanting, the stars are less numerous, and the 
depth of the firmament must, therefore, be considered less. 
In the following year appeared one of Herschel's most 
important papers on the constitution of the visible uni- 
verse. f He presents a "theoretical view" in the follow- 
ing words: "Let us then suppose numberless stars of 
various sizes scattered over an indefinite portion of space 
in such a manner as to be almost equally distributed 
throughout the whole. The laws of attraction, which no 
doubt. extend to the remotest regions of fixed stars, will 
operate in such a manner as most probably to produce the 
following remarkable effects," which he styles "the for- 
mation of nebulas" — an expression which reflects the 

* Of Some Observations Tending to Investigate the Constitution of the 
Heavens, Phil. Trans., vol. Ixxiv, 437. 

t On the Construction of the Heavens, Phil. Trans., 1785, vol. Ixxv, p. 213. 



600 BE. LAMBERT AXD SIR WILLIAM HERSCHEL. 

opinion then held by him, that all the nebulae are clusters 
of stars like our own firmament, but all external to it, 
and in many cases " unresolvable " only in consequence of 
their enormous distances. He conceives that forms like 
the following must result: Form 1. A large star draws 
surrounding smaller ones toward it, and a cluster with a 
globular figure results. Form 2. A few stars, closer 
together than the average, constitute a central attractive 
group. From this process a great variety of shapes 
might result. Form 3. Produced by the "composition 
and repeated conjunction of both the foregoing forms." 
The result would be "long-extended, regular or crooked 
rows, hooks or branches." Form 4. Still more extensive 
combinations, when, at the same time that a cluster of 
stars is forming in one part of space, there may be an- 
other collecting in a different, but perhaps not far distant 
quarter, which may occasion a mutual approach toward 
their common centre of gravity."* Form 5. "As a 
natural consequence of the former cases, there will be 
formed great cavities or vacancies by the retreat of the 
stars toward various centres which attract them." 

He then replies to certain objections which might be 
offered against such conceptions. Such an arrangement, 
it might be said, tends to "general destruction by the 
shock of one star's falling on another." He replies: 1. 
The Creator has the power to avert such destruction, and 
conserve the celestial order by some method not known to 
us. 2. "The indefinite extent of the sidereal heavens 
must produce a balance that will effectually^ secure all the 
great parts of the whole from approaching to each other." 
The stars may also have had an original force of pro- 
jection, and this would secure perpetuity to each cluster 
"at least for millions of ages." "Besides, we ought, per- 

* These specifications are similar to those presented in the present work, 
Part I, ch. ii, except that thej- are applied to the congregation of stars instead 
of the aggregation of nebulous matter. 



SIR WILLIAM HERSCHEL's RESEARCHES. 601 

haps, to consider such clusters and the destruction of now 
and then a star, in some thousands of ages, as perhaps the 
very means by which the whole is preserved and renewed. 
These clusters may be the laboratories of the universe, if 
I may so express myself, wherein the most salutary reme- 
dies for the decay of the whole are prepared." 

Herschel then presents further details of results of 
star gauging, with confirmations of his former conclusions 
respecting our star cluster. 

2. Nebular Studies. — The unequal distribution of the 
nebulas receives his attention. Those regions in which the 
nebulae are most evenly scattered possess " a certain air of 
youth and vigor." The stellar bodies have not yet had 
sufficient time to withdraw themselves from wide spaces 
in their process of general aggregation. The nebular forms 
of the first and second class " probably owe their origin to 
what may be called the decay of a great compound nebula 
of the third class; and the subdivisions which have hap- 
pened to them in length of time have occasioned all the 
small nebulae which spring from them to lie in a certain 
range, according as they are detached from the primary 
one. In like manner, our system, after numbers of ages, 
may very probably become divided so as to give rise to a 
stratum of two or three hundred nebulge; for it would not be 
difficult to point out so many beginning or gathering clus- 
ters in it." Some parts of our firmament indeed, begin 
to show the "ravages of time," for the stellar bodies have 
beeft almost completely withdrawn from them. One of 
these remarkable "openings in the heavens" exists in 
the Scorpion, Other parts present a wonderful degree 
of "purity or clearness," and this is the general aspect 
of the sky "when we look out of our stratum at the 
sides." 

In this connection he enumerates several other Milky 
Ways or firmaments, some of which are supposed to be 



602 DR. LAMBERT AXD SIR WILLIAM HERSCHEL. 

much larger than our own, and one of which presents the 
aspect of a ring of stars. " Planetary nebulte " are par- 
ticularly noticed. They present, unlike ordinary nebulae, 
a uniform brightness from side to side. Their "light, 
however, seems to be of a starry nature, which suffers not 
nearly so much as the planetary discs are known to do 
when much mao^nified." Their lio-ht is uniform and vivid. 
Their diameters are too small for nebulse; and their 
brightness is too persistent under high powers, to be of a 
planetary character, while it is not intense enough for 
fixed stars. They are probably nebulse; "but then they must 
consist of stars that are compressed and accumulated in 
the highest degree. If it were not perhaps too hazardous 
to pursue a former surmise of a renewal in what I fig- 
uratively called the laboratories of the universe, the stars 
forming these extraordinary nebulse, by some decay or 
waste of nature being no longer fit for their former pur- 
poses, and having their projectile forces, if any such they 
had, retarded in each other's atmosphere, may rush at last, 
together, and either in succession, or by one general and 
tremendous shock, unite into a new body. Perhaps the 
extraordinary and sudden blaze of a new star in Cas- 
siopoeia's Chair, in 1572, might possibly be of such a 
nature."* 

Hitherto, Herschel had considered all the nebulae as 
merely clusters of stars. Some of them had been actually 
resolved into points of light, and their resolvability seemed 
to bear a relation to the telescopic power employed. *It 
was perfectly natural, therefore, to conclude ihat all would 
show resolvability if instruments sufficiently powerful 
could be brought into use. But in 1791f he began to 

*Herschers conception of the form of our firmament is illustrated in Plate 
viii of the volume of Transactions last cited. These figures are reproduced in 
Newcomb"s Popular Astronomy, pp. 469 and 481. For a popular and brilliant 
exposition of Herschel's views, see Prof. J. P. Nichol: Views of the Architecture 
of the Heavens, Amer. ed., 1842. 

+ On Nebulous Stars Properly So-called. Phil. Trans., 1791. 



SIR WILLIAM HERSCHEL'S RESEARCHES. 603 

suspect that certain cases of diffused luminosity could not 
arise from the blended light of numerous distant suns. The 
" nebulous stars," now first observed, present a bright 
central body surrounded by a faint light cloud. Now if 
this envelope consists of stars, they must be either too 
small to be regarded as stars, properly speaking, since 
while the central star is perfectly distinct they are indis- 
tinguishable, or otherwise, the central star must attain a 
magnitude which surpasses credence. This subject, even 
while researches of diverse nature occupied his time,* 
seems to have been kept before his attention. In 1811 he 
presented one of the most important papers of the re- 
markable series which resulted from his highly original 
investigations.! He here formally announces a gradual 
change of opinion in regard to the resolvability of some 
of the nebula. The most primitive nebular condition is 
represented, he thinks, by the simple diffused nebulosities, 
of which he has determined the positions of fifty-two. 
The brighter portions he regards as more dense, and the 
central condensation is due to the action of gravity. 
Some nebulae seem to have more than one centre of attrac- 
tion; and some, it may be, are even undergoing a process 
of disintegration. The spheroidal forms would naturally 
result from the action of a central attractive force. There 
are many in which the central brightness indicates the 

* In 1795 he commuriicatecl a paper On the Construction of the Sun and Fixed 
Stars^ in which he recorded the opinion that many of the stars are habitable, 
since some are too close to admit of planetary orbits, and that if not habitable 
in the character of suns "many star?, unless we would make them mere useless 
brilliant points, may themselves be lucid planets, perhaps unattended by satel- 
lites." In 1805 he discussed Tlie Direction and Velocity of the Motion of the Sun 
and Solar System. (See also Phil. Trans., 1T83, On the Proper Motion of the Sun 
and Sclav System.) The conclusion of his researches on this point is that the sun 
is moving toward the constellation Hercules. In 1806 he read a paper On the 
Quantity and Velocity of the Solar Motion. 

■\ Astronomical obsei'vations relating to the construction of the heavens, ar- 
ranged for the purpose of a critical examination, the result of which appears 
to throw some neiv light upon the organization of the celestial bodies. 



604 DR. LAMBERT AN^D SIR WILLIAM HERSCHEL. 

seat of principal attraction. Some even have a distinct 
central nucleus. The various degrees of condensation are 
supposed to take place successively in the same nebula. 

The appearance of certain very regular nebulae with 
extensive branches suggests various queries. Do not the 
branches connected with a nucleus resemble the zodiacal 
light connected with our sun? May not portions of 
branches collect into a planetary form and revolve around 
the central nucleus [of the nebula], having themselves a 
rotary motion in consequence of the inequality and irregu- 
lar position of the different branches? Seven nebulae are 
mentioned which seem to have approached very near to 
final condensation. The spheroidal form which prevails 
among nebulae is something from which a rotation on their 
axes may be inferred. 

That nebulae do really undergo successive changes, 
Herschel concludes not only from a comparison of different 
nebulae with each other, but from a comparison of his own 
observations made on the nebula of Orion at this time, 
with those which he himself made thirtj^-seven years be- 
fore. This nebula he thinks is certainly nearer than the 
stars of the seventh or eighth magnitude, and it may pos- 
sibly not be more distant than those of the third. 

He suggests, at this time, the following gradation 
of nebular existences: 1. Diffused nebulosity, invisible 
until partially condensed. 2. Planetary nebulae, with uni- 
form light. 3. Stellar nebulae, having a bright central 
nucleus. 4. A complete star, all the nebulous matter 
being condensed. 

In 1814 Herschel's views had become still more clearly 
defined.* He shows that clusters of stars are gravitating 
together like nebulous matter. Some stars are attracting 

* Astronomical obsei'vations relating to the sidereal part of the heavens, and 
its connection ivith the nebulous part ; arranged for the purpose of a critical 
examination. Phil. Trans., 181-', p. 248. 



SIR WILLIAM IIERSCHEL's RESEARCHES. 605 

patches of nebulous matter to themselves. Stars and 
nebuLne seem to be drawn together by mutual attraction. 
By additions of matter there may be thus a real growth 
of stars. He mentions one hundred and fifty instances 
in which clusters of stars, by being more dense toward the 
centre, manifest a tendency like that in nebula?. He sug- 
gests now, the following gradation in nebular development: 
1. Globular nebula. 2. Nebula with nucleus. 3. Nebu- 
lous star. 4. Distinct star surrounded by a nebulosity. 
5. The perfect simple star. 

In 1817 and 1818* Herschel returned to the work of 
sounding the depths of the firmament, basing his conclu- 
sions on the assumption that the distances of the stars are 
on the whole inversely proportional to their brightness. 
He concludes, as the result of these renewed researches, 
that his former determinations do not require material 
alteration, and that little further knowledge is attainable 
in reference to the form and depth of our firmament, 
especially in the direction of the Milky Way.f 

* Astronondcal observations and experiments tending to investigate the local 
arrangemeni of the celestial bodies in space and to determine the extent and 
condition of the Milky Way. Phil. Trans., 1817, p. 302. Astrotiomical observa- 
tiotis and experiments selected for the purpose of ascertaining the relative dis- 
tances of clusters of stars, and of investigating how far the power of our tele- 
scopes may be expected to reach into space when directed to atnbigmiis celestial 
objects, Phil. Trans., 1818. 

tSir John Herschel, in communicating to the Royal Soeiety, Observations of 
nebu'ce and clusters of stars made at Slough with a twenty-feet reflector, between 
the years 1825 and 1S33 (Phil. Trans., Nov. ?1, 1833) supplies an appendix to his 
father's researches. He transmits a catalogue of 2,500 nebuhe and clusters, of 
which 2,000 had been previously reported by his father. The most remarkable 
nebulae were accompanied by sketches. "Among these are represented some 
very extraordinary objects which have not hitherto sufficiently engaged the at- 
tention of astronomers, and many of which possess a symmetry of parts and a 
unity of design strongly marking them as sj'stems of definite nature, each com- 
plete in itself, subservient to some distinct, though to us inscrutable purpose." 



CHAPTER IV. 

LAPLACE'S SYSTEM OF THE WORLD.* 

France possesses an iaimortal work, L' Exposition du Systeme da Monde., in 
which the author has combined the results of the highest astronomical and 
mathematical labors, and presented them to his readers free from all processes 
of demonstration. The structure of the heavens is here reduced to the simple 
solution of a great problem in mechanics ; yet Laplace's work has never yet been 
accused of incompleteness and want of profundity.— Humboldt. 

§ 1. PRELIMINARY VIEWS OX XEBUL^ AXD GENERAL 
PHYSICAL ASTROXOMY. 

THE purpose of this work is to present in popular style 
the general results of astronomical research. It de- 
scribes the apparent movements of the heavenly bodies and 
their real movements, proceeding thence to an exposition 
of the mechanical laws of their movements, and of the 
theory of universal gravitation, and of its operation in 
the forms and interactions of the planetary masses. The 
last book is devoted to an epitome of the history of 
astronomy, in the last chapter of which the author pre- 
sents some general reflections, and records some remark- 
able anticipations of future discoveries. 

He expresses the opinion that some of the other 
planets may be the abodes of animals and plants analo- 
gous to those which exist upon the earth ; but the great 
diversities of temperature must necessitate a remarkable 
diversity of organization. The physical relations which 

* Pierre le Marquis de Laplace : Exposition dn Systeme du Monde, 5me ed. 
revue et augmentee par Vauteur. Paris, 1824. 4to, pp. 419. The original edition 
was published in two vols. 8vo. Paris, 1796, and the sixth edition, containing a 
eulogy by Baron Fourier, in 4to, 1835, eight years after Laplace's death. An 
English translation exists. 

606 



PKELIMINARY VIEWS ON NEBUL.E, ETC. 607 

exist among the planets shed much light upon their 
origin. The astonishing number of uniformities enum- 
erated could not arise from any irregular causes. Sub- 
jecting the question to computation, it appears that the 
probability is more than two hundred trillions to one that 
these harmonies are not the result of chance. "It is 
necessary, therefore, to assume that one primitive cause 
has directed all the planetary movements." Another re- 
markable fact is the small eccentricity of the planetary 
orbits. There is no intermedium between the planets and 
the comets in this respect. "What is that primitive 
cause ? I shall offer a hypothesis in the note at the end 
of this work, which appears to me to result, toith great 
probability y from the preceding phenomena ; but I pre- 
sent it with the diffidence which ought to inspire every- 
thing which is not the result of observation or of calcu- 
lation." 

Before proceeding to reproduce the substance of the 
note, I think it proper to follow the author in some of his 
general considerations, since, as will appear, they are 
connected with his hypothesis, although not made to 
constitute a part of it. Some of the phenomena of our 
system Newton confessed his inability to refer to the prin- 
ciple of gravitation. Such were the uniformity in the 
directions of planetary movements, the nearly circular 
forms of the orbits, and their remarkable conformity to 
one plane. These adjustments Newton, in his general 
scholium,* pronounces to be "the work of an intelligent 
and all-powerful Being." "But," asks Laplace, "might 
not these arrangements be an effect of the laws of 
motion ; and might not the supreme intelligence which 
Newton invoked have caused them to depend on a more 

* Laplace in a note says; "This scholium is not found in the first edition of 
Newton's work. It appears that Newton to that time was devoted exclusively 
to the mathematical sciences which, unhappily for them and for his own fame, 
he too soon abandoned," 



608 Laplace's stste:m of the world. 

general phenomenon ? Such is, according to our con- 
jectures, that of a nebulous matter dispersed in masses 
through the immensity of the heavens. Is it possible 
then to affirm that the conservation of the planetary sys- 
tem enters into the views of the author of nature ? The 
mutual attraction of the bodies of this system cannot 
alter its stability, as Newton himself demonstrated ; but 
there may be in celestial space some other fluid than 
lighty its resistance, and the diminution which its emis- 
sion causes in the mass of the sun, must at length destroy 
the arrangement of the planets, and, to maintain it, a re- 
constitution would undoubtedly become necessary. But 
do not the numerous species of extinct animals whose or- 
ganization Mr. Cuvier has determined with such rare 
sagacity, in the numerous fossil bones which he has de- 
scribed, indicate a tendency in nature to change even 
those things which appear most permanent ? The gran- 
deur and importance of the solar system ought not to 
constitute an exception to this general law, for they exist 
only relatively to our insignificance, and this system, vast 
as it seems, is only an insensible point in the universe. 
Glance over the history of the progress of the human 
mind and its errors, and we see there final causes continu- 
alh' retreating before the bounds of human knowledge. 
Those causes which Xewton removed to the limits of the 
solar system were, even in his time, located in the atmos- 
phere for the explanation of meteors. They are nothing, 
then, in the eyes of the philosopher, but the expression 
of our ignorance of true causes."* Casting our eyes be- 

* This passage shows that by "final causes'' Laplace understood that der- 
nier resort to which we all come at last — the most learned philosopher as well 
as the mediaeval religionist — where actual knowledge can furuish no further ex- 
planation, and judgment and reason together fall back on an inscrutable world- 
making agency. "Final causes "'—last causes — are simply the antithesis of 
known and explicable causes — that is, explicable as to their modes of operation. 
Xow, in this sense, it is ob^iously imsafe to declare at any stage in the exten- 
sion of our knowledge, that mind will make no further advance, and that all 



PKELIMINARY YIEWS OK NEBULiE, ETC. 609 

yond the limits of the solar system, the changes observed 
in the color and brightness of certain stars show that 
the principle of permanence cannot be of universal ap- 
plication. The temporary star described by Tycho Brahe 
convinces us that in the depths of space revolutions occur 
which surpass beyond computation all which take place 
on the surface of the earth. As this star did not cease to 
exist after it became invisible, we are taught that other 
equally considerable, but dark and invisible, bodies, may 
exist in number perhaps equal to the number of the stars. 
The heavenly bodies are undoubtedly assembled in groups. 
The group to which our sun belongs seems to encircle the 
heavens as a Milky Way. Like the Milky Way, many of 
the nebulae are probably assemblages of stars which to a 
beholder from their interiors would seem like other galaxies. 

beyond is simply the product of "final causation"— that is, of divine causation. 
If this were the only conception of final cause, we should truly be compelled to 
abandon the search for it; and yet every intelligent person would feel con- 
strained to admit that somewhere is an ultimate limit to the activity of sec- 
ondary causation (physical antecedence and sequence) and a real beginning pro- 
ceeding out of some activity which is supernatural. 

But the term "final cause" has a more legitimate signification which fur- 
nishes something worth contending for. It implies, that in the exertion of that 
primitive supernatural causation there must have been some ^wr/?ose present. 
It implies, therefore, that in the endless series of events which flow from that 
primitive causal act that primitive purpose is ever unfolding and ever present. 
It does not imply that in any specific result finite intelligence can certainly 
eliminate the specific divine purpose; but it does imply that in every specific 
result there is some divine purpose. 

If, as modern physics tend to conclude, the physical forces are only the 
manifestations of a supreme will, exerted according to a predetermined method, 
then each specific and individual result will associate with it directly, the neces- 
sary conception of purpose, just as that conception is always inseparable from 
primitive causation. 

It is only a supei-ficial and unsatisfactory science which contents itself with 
the observation and collocation of naere phenomena, and the determination of 
the methods according to which they emerge into existence. The human mind 
demands causes — and not alone physical causes or mere uniform antecedents — 
but real ultimate causes, "metaphysical causes." I maintain, therefore, that 
every normally active intellect tends toward metaphysical conceptions of 
material phenomena. (See an article by the present writer on The Metaphysics 
of Science, in North American Review, Jan., 1880, also, Sparks from a Geolo- 
gisfs Hammer, pp. ;i58-85.) 
39 



610 

Herschel has followed the progressive changes in neb- 
ula, as we trace the life history of a tree, by observation 
of successive states contemporaneously existing in differ- 
ent trees. His classification of nebulte is then cited,* and 
particular attention is directed to the stellar nebulae in 
which a well marked nucleus, or several of them, has 
already come into existence. The atmosphere of each 
nucleus seems to be condensing upon the centre. When 
the matter condenses uniformly, a planetary nebula re- 
sults. The phenomena indicate with great probability a 
progressive transformation into stars, and imply that exist- 
ing stars were at a former time nebulae. *' Thus we 
descend through the process of condensation of nebulous 
matter to the consideration of the sun surrounded at a 
former time by a vast atmosphere, a conception to which 
T have already been led by a consideration of planet- 
ary phenomena, as will appear in the note before referred 
to. A coincidence so remarkable in pursuing opposite 
courses gives to the existence of this former condition of 
the sun a high degree of probability."! 

"In connecting the formation of comets with that of 
nebulae, we may regard them as small nebulse wandering 
from solar system to solar system, and formed by the 
condensation of nebulous matter dispersed with so great 
profusion through the universe. Comets would thus be, 
in relation to our system, ichat aerolites are in relation 
to the earth, to %ohich they are strangers.'''' * * * ^'This 

* See above, p. 604. 

+ It is often alleged by the opponents of the nebular theory that its author 
— meaning Laplace — placed a lo\s' estimate on its importance and probabilitj', 
and therefore hid it away in a note at the end of the volume. But such expres- 
sions as that above quoted, and others hereafter to be quoted, indicate that 
Laplace regarded his hypothesis as possessing great strength. Moreover, many 
of the accessory facts and reasonings are embodied in the leading discussions 
of his work. More than a quarter of a century after the publication of the 
work, the author referred to this theory with a degree of complacency which 
showed that years had ripened the conviction of its tenability and value.— ife- 
canlque Ctleste, torn, v, 346. 



HYPOTHESIS OF GEKESIS OF SOLAR SYSTEM. 611 

hypothesis explains in a happy manner the enlargement 
undergone by the heads and tails of comets in their ap- 
proach to the sun; the extreme rarity of their tails, which, 
notwithstanding their immense thickness, do not sensibly 
diminish the light of the stars seen through them; the 
varied directions of the motions of comets, and the high 
eccentricity of their orbits." 

The movements revealed in the solar system are exceed- 
ingly complicated. Like the planets, however, the stars 
are also in motion. The sun describes an epicycloidal 
orbit around the centre of gravity of the universe. Ages 
must be demanded to enable us to determine precisely the 
movements of the sun and the other stars: but observa- 
tion has already shown that the stars have real motions, 
while some of the double stars are proved to possess orbital 
movements about a common centre of gravity; and even 
the nebulae, especially that in Orion, have .been observed 
in progress of change. Such phenomena will present to 
the astronomy of the future its principal problems. 

§ 2. HYPOTHESIS TOUCHIXa THE GENESIS OF THE 
SOLAR SYSTEM. 

We come now to the contents of the celebrated Note. 
Its scope embraces only the solar system, but we have 
seen that the grounds of the hypothesis are supplied in 
the facts of positive astronomy in all its range. Buffon 
attempted to explain the origin and phenomena of the 
solar system by supposing that a comet had struck the 
sun and detached a torrent of matter which gathered in 
planetary globes more or less removed, and in course of 
time became cold and opaque. While this hypothesis 
explains many of the phenomena cited, it does not ex- 
plain why the planet rotates in the same direction as its 
orbital motion, nor why the eccentricity of its orbit should 
be so low. Theory shows that if it were thrown off from 



612 LAPLACE'S SYSTEM OF THE WORLD. 

the sun it would periodically return nearly to the same 
point. Finally, the hypothesis of Buffon does not explain 
the abrupt transition in respect to eccentricity between 
the orbits of the planets and those of the comets. 

1. Former Expansion of the Solar Atmosphere. — 
*' Whatever the nature of the common cause of the planet- 
ary movements, since it has produced or directed these 
movements it must of necessity have embraced all the 
planetary bodies; and, considering the prodigious dis- 
tances which separate them, it could have been nothing 
else than a fluid of immense extent. In order to have 
given them an almost circular motion in a uniform direc- 
tion about the sun, this fluid must have surrounded the 
solar body like an atmosphere. The consideration of the 
planetary movements leads us, then, to think that, in con- 
sequence of its excessive heat, the atmosphere of the sun 
extended formerly beyond the orbits of all the planets, 
and that it contracted by degrees to its present limits." 

"In this primitive state of the sun it resembled the 
nebulae which the telescope reveals to us composed of a 
more or less brilliant nucleus, surrounded by a nebulosity 
which, by condensation upon the surface of the nucleus, 
transforms it into a star. If, by analogy, we conceive all 
the stars formed in this manner, we can imagine their 
former state of nebulosity itself preceded by other states 
in which the nebulous matter was more and more diffuse, 
the nucleus being less and less luminous. We arrive thus, 
in receding as far as possible, at a nebulosity so diffuse that 
its existence is barely imaginable." 

Mitchel long since remarked that the grouping of the 
Pleiades could not be the result of chance; and the same 
may be said of all clusters of stars. They must be "the 
effects of a primitive cause or general law of nature. 
Such groups are the necessary result of the condensation 
of nebulas about numerous nuclei." 



i 



HYPOTHESIS OF GEN'ESIS OF SOLAR SYSTEM. 613 

2. Formation and Abandonment of Zones of Vapor, 
— " But how did the solar atmosphere determine the mo- 
tions of rotation and revolution of the planets and satel- 
lites? If these bodies had been profoundly immersed in 
this atmosphere, its resistance would have caused them to 
fall upon the sun. We are compelled to assume, there- 
fore, that the planets have been formed at their successive 
limits by the condensation of zones of vapors which, in 
the process of cooling", it must have abandoned in the 
plane of its equator." 

" Let us recall now the results presented in the tenth 
chapter of the preceding book. The atmosphere of the 
sun could not extend outward indefinitely; its limit would 
be the point where the centrifugal force due to its move- 
ment of rotation would counterbalance gravitation. But, 
in proportion as cooling contracted the atmosphere, and 
condensed at the surface of the body the molecules located 
in that region, the movement of rotation increased by 
virtue of the principle of areas." The centrifugal force 
due to increased rotation becoming increased, the point 
where gravity equals it w^ould be nearer the centre. In 
short, a process of annulation would begin and proceed.* 

The zones of vapors necessarily abandoned "must 
probably, by their condensation and the mutual attraction 
of their molecules, have formed different concentric rings of 
vapors circulating about the sun. The mutual friction of 
the molecules of each ring must have accelerated some 
and retarded others, until all should have acquired the 
same angular motion. Thus the actual velocities of the 
molecules most remote from the sun have been the greater. 
The following cause must have further contributed to this 
difference of velocities: The molecules farthest removed 
from the sun, and which, in the progress of cooling and 
condensation, must have formed the exterior portion of 

* In the way which I have elsewhere explained, following Laplace. 



614 LAPLACE'S SYSTEM OF THE WORLD. 

the ring, have always described areas proportional to the 
times, since the central force which actuated them has 
been constantly directed toward the solar centre; but this 
constancy of areas demands an acceleration of velocity in 
proportion as the molecules are condensed. It is apparent 
that the same cause must have diminished the velocity of 
the molecules which constitute the interior border of the 
ring." 

3. Rupture and Planetation of Hings. — Proceeding 
to the subsequent history of a ring, the author shows that 
the conditions of its permanence can very rarely exist. 
" Almost always each ring of vapors must have broken up 
into numerous masses, which, moving with a nearly uni- 
form velocity, must have continued to circulate at the 
same distance around the sun. These masses must have 
taken a spheroidal form, with a motion of rotation in the 
same direction as their revolution, since the inner mole- 
cules [those nearest the sun] would have less actual 
velocity than the exterior ones. They must then have 
formed as many planets in a state of vapor. But if one 
of them was sufficiently powerful to unite successively, by 
its attraction, all the others around its centre, the ring of 
vapors must have been thus transformed into a single 
spheroidal mass of vapors circulating around the sun 
with a rotation in the same direction as its revolution. 
The latter case has been the more common, but the solar 
system presents us the first case in the four small planets* 
which move between Jupiter and Mars." 

The author then traces the same process in the history 
of these planetary globes of fire mist. "The regular dis- 
tribution of the mass of the rings of Saturn around his 
centre and in the plane of his equator, results naturally 
from this hypothesis, and without it would be inexpli- 
cable. These rings appear to me to be proofs ever-exist- 

* All the asteroids then known. 



HYPOTHESIS OF GENESIS OF SOLAR SYSTEM. 615 

ing of the primitive extension of Saturn's atmosphere 
and its successive retreats." Thus the remarkable uni- 
formities in planetary conditions and movements "flow 
from the hypothesis which we offer, and give it a strong 
probability of truth." 

The diverse inclinations and eccentricities of the plan- 
etary orbits are attributed to the "numberless variations 
which must have existed in the temperature and density 
of the different parts of the large masses." 

4. Relations of Cornets and Zodiacal Light. — "In 
our hypothesis," the author concludes, "the comets are 
strangers to the planetary system."* The great eccen- 
tricity of their orbits, as well as their various inclinations, 
is a consequence of the present hypothesis. " The at- 
traction of the planets, and perhaps also the resistance 
of the ethereal medium must have changed many comet- 
ary orbits into ellipses whose longer axis is much less 
than the radius of the sun's activity." "If any comets 
penetrated the atmospheres of the sun and planets during 
the time of their formation, the former must have been 
precipitated in spiral paths upon these bodies, and by 
their fall have displaced the planes of the orbit and of the 
equators of the planets from the plane of the solar 
equator." 

"If, in the zone abandoned by the atmosphere of the 
sun, there existed molecules too volatile to be united 
among themselves or with the planets, they must have 
continued to circulate about the sun under an aspect such 
as the zodiacal light presents, but with too great tenuity 
to oppose any sensible resistance to the various bodies of 
the planetary system, a result which would also flow from 
a motion in the same direction as that of the planets." 

5. Lunar Synchronistic Motions. — "A profound ex- 
amination of all the circumstances of this system increases 

* See the full passage quoted above, p. 182. 



616 Laplace's system of the avorld. 

still farther the probability of our hypothesis. The primi- 
tive fluidity of the planets is clearly indicated by the 
flattening of their figure." The vicissitudes of geological 
history and the nature of the succession of animals and 
plants upon the earth, similarly testify to a progressive 
reduction of temperature. 

" One of the most singular phenomena of the solar sys- 
tem is the rigorous equality observed between the an- 
gular motions of rotation and the orbital revolutions of 
the several satellites. The probability is as infinity to 
one that this is not the result of chance. The theory of 
universal gravitation causes this improbability to disap- 
pear by showing that it suffices for the existence of this 
phenomenon that in the beginning these movements should 
have been but slightly different. At that time the at- 
traction of the planet established between them a perfect 
equality, but at the same time, it gave birth to a periodic 
oscillation of the axis of the satellite directed toward the 
planet. The extent of this oscillation would depend on 
the primitive difference of the two movements. The ob- 
servations of Mayer on the libration of the moon, and 
those which MM. Bouvard and Nicollet have made on this 
subject at my request, not having led to the discovery of 
such an oscillation, the difference on which it depends 
must have been very small. This circumstance indicates 
with extreme probability a special cause which originally 
embraced this difference within very narrow limits where 
the attraction of the planet has been able to establish 
between the mean motions of rotation and revolution a 
rigorous equality, and has subsequently acted until it de- 
stroyed the oscillation to which this equality had given 
origin. Both these effects result from our hypothesis, for 
we conceive that the moon in the state of vapor, assumed 
through the powerful attraction of the earth, the form of 
an elongated spheroid whose longer axis was directed con- 



HYPOTHESIS OF GENESIS OF SOLAR SYSTEM. 617 

stantly toward this planet. This would result from the 
readiness with which vapors yield to the feeblest forces 
acting upon them. Terrestrial attraction continuing to 
act in the same manner as long as the moon was in a fluid 
state, must at length by continually approximating the 
periods of the two motions of this satellite, have caused 
their difference to fall within the limits where their, rigor- 
ous equality began to be established. Subsequently, this 
attraction must have destroyed, little by little, the oscilla- 
tion which this inequality produced in the longer axis of 
the spheroid directed toward the earth. In the same way, 
the fluids which cover this planet have destroyed by their 
friction and by their resistance the primitive oscillations 
of its axis of rotation ; for this is now subjected only to 
the nutation resulting from the actions of the sun and 
moon." 

The well known remarkable relation between the 
orbital motions of Jupiter's satellites is explained on the 
nebular hypothesis in a manner precisely similar. 



CHAPTEE T. 

SYSTEMATIC RESUME OF OPINIONS. 

THE foregoing sketch of opinions shows that 
1. The two fundamental conceptions of nebular 
cosmogony have been in existence ever since the dawn of 
Greek philosophy. These are : (1) The conception of 
widely extended, unorganized, homogeneous matter, which 
the Greeks called Chaos, and most late writers have iden- 
tified with the 7iehular condition of matter ; (2) A vorti- 
cal movement as the occasion and cause of the differ- 
entiations of atoms and parts, and the organization of 
structural order. 

2. The theory as here accepted is most nearly that 
which was promulgated by Laplace ; but it contains prob- 
ably a greater amount of matter which was original with 
Kant. 

3. The modern theory \vas impossible until Newton 
had demonstrated the principle of universal attraction, 
and Newton and the brilliant mathematicians of the 
eighteenth century had settled analytically the dynamical 
principles of the solar system, and Sir William Herschel 
had given the world some adequate knowledge of nebular 
and firmamental relations. Nor was the modern theory 
possible until the mechanical doctrine of h^at, and the 
general doctrine of the conservation of energy, and the 
kinetic theory of gases had been firmly established. A 
whole constellation of original thinkers have therefore 
brought their respective contributions to the perfection 
and confirmation of the generally accepted doctrine of 
cosmogenesis. 

618 



VORTICAL MOTIOI^. 619 

The part which the several cosmogonic systems and 
conceptions contributed to the modern theory may per- 
haps be most intelligibly set forth in an enumeration of 
the constitutive principles of general nebular cosmogony. 

1. A HOMOGENEOUS MEDIUM. 

Chaos. 1. A Continuous substance. Anaxagoras {Homceomeria) 
Descartes. Compare the "primitive fluid" of Sir W. Thomson. 

2. An Atomic medium. Leucippus, Democritus, Epicurus, Lu- 
cretius aud other Greek atomists. Newton aud most moderns. 
Compare the "monads" of Leibnitz. 

3. Dynamical molecules. Boscovich, ? Faraday. Compare the 
"vortical atoms" of Sir W. Thomson. 

Solar emanation. Kepler. But the sun and planets are supposed 

already existent. 
Plenum of matter hecoming differentiated into Particles. Descartes. 
Ethereal Fluid. Leibnitz. But the planets already assumed to be 

in existence. 
An infinitude of Atomic Vortices. Swedenborg. 
Primitive fluid formed of all the matter of the solar system dissolved 

into its elements. Kant. 
Nehulous Matter existing in finite regions of space. Huygens, Sir 

William Herschel, Laplace. 
Disappearance of the medium on Formation of Planets. Kant, 

Laplace. 

3. VORTICAL MOTION. 

Revolution of the Heavens. Egyptians, Chaldjeans and Greeks. 
Rotation of the Earth. Hicetas, Ecphantus, Ileraclides, Cusanus. 
Revolution of the Earth. Aristarchus, Seleucus, Archimedes, Arya- 

batta, Copernicus. 
Elemental , Vortices. 1. Inaugurated hy TJie Mind. Anaxagoras. 

TorricelH, Galileo, Descartes, Swedenborg. Compare "Vortical 

Atoms " by Sir William Thomson. 

2. Existing from eternity. Leucippus, Democritus. 

3. Originated hy self determination. Epicurus, Lucretius, Gas- 
sendi, Leibnitz, Rosmini, Campanella. 

Systemic Vortices. 1. One Solar Vortex. Kepler. 
2. Planetary and Solar Vortices. 

(a.) Origin not explained on Mechanical Principles. Descar- 
tes, Leibnitz, Swedenborg, Wright, Lambert. 



620 SYSTEMATIC RESUME OF OPIXIOJi"S. 

(b.) The result of mechanical action. Kant, Laplace (except 
solar rotation). 
JVebular Vortices. Kant, Herschel, Laplace. 
{Firmamental Rotation. Wright, Kant, Lambert.] 
Orhital 3Iovement of Our Sun in Space. Laplace, Herschel (not 
stated to be orhital). 

3. UN^m^RSAL CONCURRENCE OF MATTER. 

Love, imth its antithesis, Hate. Empedocles. 

Cosmical Magnetism. Kepler (who utilized attraction and repul- 
sion), Swedenborg. 

Universal Attraction. Newton, Wright, Kant, Lambert, Herschel, 
Laplace. 

Pressure and Impulse. 1. From a cosmical fluid. Descartes, 
Leibnitz. 
2. Storm of '^ ultramundane corpuscles.''' Le Sage.* 

Consequent central Condensation. Kant (except at the centre), 
Herschel (in nebulae). 

Consequent Heat and Luminosity. Lichtenberg, Kant. 

4. THERMAL RADIATION AND CONTRACTION. 

Condensation around Solar and Planetary Centres. Kant, Laplace. 
Heat and Luminosity maintained. Helmholtz, etc. 

5. ANNULATION. 

One Equatorial Ring accumulated. Swedenborg. 
Saturnian Ring thrown off (possibly other planetary rings). Kant. 
Successive Solar Equatorial Rings abandoned. Laplace. 
Stratification of Rings. Kant (in respect to Saturn's), Laplace. 
Saturnian Rings hut Swarms of small Satellites. Cassini, Kant, 

Peirce, Clerk-Maxwell. 
TJie Zodiacal Light a similar Ring. Kant, Laplace. 
Annulation in existing Nebulm. Herschel. 

6. SPHERATION OF RINGS. ' 
One Ring disrupted formed the Several Planets, which icere throivn 

outward to their respective positions. Swedenborg. 
Each of Several Rings gathered into a planetary mass. Laplace. 

* Le Sage : Lucrece Neivtonien : Traite de Physique Meeardque, Geneva, 1818. 
See also Constitution de la Matiere, etc.. par le P. Leray, Paris, 1869, and Tait's 
Recent Advances in Physical Science, 299. 



CYCLES OF COSMIC EXISTEN-CE. 621 

In one instance a ring resulted in, Numerous Asteroids. Laplace. 
The Asteroids may have resulted from a Stratified Ring. 

7. EFFECTS OF PERTUKBATIVE ATTRACTIONS. 

Inclinations of Planetary Axes. Kant, Laplace (who also appeals to 

cometary precipitation). 
Eccentricities of Orbits. Laplace. 

8. DISLOCATIONS OF PLANETARY CRUSTS. 
Orographic Inequalities caused hy confined gases. Leibnitz, Kant. 

9. GENERALIZATION OF COSMIC HISTORY. 

Successive Stages of Star and Planet formation from a nebula — a 
planet a cooled sun. Leibnitz, Kant, Herschel, Laplace. 

Jupiter in an early stage of development. Kant. 

The Moon in a fossilized condition, Frankland.* 

Other planets habitable, or destined to be so. Kant, Lambert, Her- 
schel, Laplace. 

The various Colors of the Stars indicative of successive Stages, 
Laplace, Secchi.t 

10. CYCLES OF COSMIC EXISTENCE. 

Decay of Worlds in one region compensated by New Organisms in 

another. Kant, Herschel. 
Occasional Revival of waning suns. Kant, Herschel. 
Resuscitation of Cosmic Organisms by Precijntation and Impact. 

Kant. 

*Proc. Boy. Inst., iv, 175. The idea was advanced in the present writer's 
Sketches of Creation^m March, 1870, Compare L. Saemann: On the Unity of 
Geological Phenomena in the Solar System, Bull, de la Soc. gdo\. de France, 4 
Feb., 1861; J. Nasmyth; On the Age of the Moon's Surface, Proc. Manchester 
Lit. and Phil. Soc, Nov. 15, 1864. 

t Secchi: Le Soleil. 



INDEX. 



Abiiey on matter in space, 58, 61, 
64,481. 

Absorption of fluids, 383; on 
moon, 403, 407 ; on Jovian sat- 
ellites, 441; on planets, 460; 
index of, 460; on the earth, 
467-9 ; on Mars, Asteroids and 
Jupiter, 472; on Venus and 
Mercury, 473. 

Acceleration, rotary, from shrink- 
age, 459; from tidal action, 
251. 

Acceleration of tide-producer^ 
240. 

Adams, J. C, on meteoric orbits, 
17; on moon's acceleration, 474. 

Adhemar, on effect of precession, 
288. 

Aeriform agents in mountain 
making, 292, 324. 

Age, of moon, 379; of Mars, 415 
-6, 470; of Jupiter, 427, 429; 
of Saturn, 443 ; of Uranus and 
Neptune, 444-8. 

Age of the world, alleged too 
great, 179-81; calculations on, 
355, 470; table of, 365. 

Ages of planets in a system, 215, 
216, 415. 

Aggregation of cosraical matter, 
66, 71, 92, 185-6; heat arising 
from, 92-4. 

Airy, Gr. B., on tides, 225; on 
change of axis, 334; quoted, 
330. 

Alcyone as fancied centre of fir- 
mament, 140. 

Alexander, Stephen, on zodiacal 
light, 25; on clusters and 



nebulaB, 146; on consistencies' 
of nebular cosmogony, 150. 

Alps, fan structure in, 308, 309. 

Amorphous nebulae, 42. 

Anaxagoras, on upheavals, 292; 
on first principle, 552. 

Andrews, E., on geological time, 
374. 

Angstrom on zodiacal light, 24. 

Annular nebulae, 45, 46. 

Annulation of nebulae, 106-19; 
involving entire nebulas, 117; 
alleged improbable, 186; con- 
ditions of, 188-9 ; according to 
Faye's speculation, 203, 209; 
denied by Spiller, 212; concep- 
tion of in cosmogony, 613, 620. 
See ''Ring." 

Anticipation of tide, 234. 

Anti-tide defined, 224; acting on 
rotation, 237; acting on incli- 
nation of axis, 245. 

Appalachian region, 315. 

Apsides, motion of, 285, 

Arago, F., on meteors, 7, 14, 16; 
on nebular changes, 92; on 
astronomical climates, 296; 
cited, 146. 

Archibald, E. D., on Siemens' 
theory, 57. 

Archimedes cited, 551. 

Aristarchus cited, 551. 

Aristotle on figure of earth, 553. 

Aryabatta cited, 552. 

Asteroidal mass, disrupted state 
of, an alleged difficulty, 176. 

Asteroids a sort of meteoric ring, 
35 ; mass of, alleged too small, 
175; origin of, in a stratified 
ring, 176; or from an intra- Jo- 
vian ring, 177, 614. 



624 



INDEX. 



Astronomical changes and plane- 
tary conditions, 278. 

Atkinson, A. S., on comet of 
1882 h, 31. 

Atmosphere, effects of low den- 
sity of, 271, 504; of moon ab- 
sorbed, 382, 407 ; homogeneons, 
411; of Mars, 504; of sun, 612. 

Atmospheric factor on moon, 410; 
feebleness of, 410 seq. ; deduc- 
tions from, 412; on Mars, 419; 
on Yenus, 420; on Mereurv. 
423; on Jupiter, 428, 430. 

August meteors, 19, 20, 33. 

Axes of planets, inclinations of, 
129 ; increased by lagging tides, 
243. 

Axis, change of position of. 334, 

B 

Babbage, C. on isothermal lines 
in crust, 275, 332. 

Bache, A. D., on ocean bottom, 
302. 

Backlund on Encke's comet, 480. 

Bakewell, R., on Xiagara gorge. 
369. 

Ball, R. S., on primitive terres- 
trial tides, 263. 

Ball^^er on slipping of crust, 311. 

Bar of Mississippi River, 453. 

Barnard, E. E.. cited, 5; on 
comet of 1862 h, 30. 

Barnard, F. A. P.. on zodiacal 
light, 25. 

Barnard, G. J., on tides. 225; on 
Mallet's theory, 319, 347; on 
terrestrial rigidity, 341. 

Barometer, height of on moon, 
411. 

Barrande, J., on colonies, 281. 

Bartlett, J. R., on ocean bottom, 
302. 

Beaumont, E. de, on a wrinkling 
crust, 295; on terrestrial cool- 
ing 296 ; on earth's age, 356. 

Beche, de la, on rock absorption. 
461. 

Beer and Maedler on moon, 385. 

Beltj T., on glaciation, 285; on 
Niagara gorge, 370. 



Bentley on habitability, 497. 
Bergeron cited, 408. 
Bernouilli, D., on tides, 225. 
Bernouilli, John, cited, 565. 
Berthelot on dissociation of mat- 
ter, 48. 
Bessey, C. E., on yellow rain, 7. 
Biela's comet, 32, 34. 
Biot on zodiacal light, 26. 
Bischof on age of the earth, 179; 

on elastic force of steam, 294; 

on rock absorption, 464. 
Bluff recession, rate of, 374, 378. 
Bode, J. E., cited, 598. 
Boiling point on moon, 412. 
Bond, Gr., on nebulse, 42. 
Bore, tidal, 400. 
Boscovich on atoms, 569. 
Boss L., on lunar maps, 385. 
Boucheporn on collision with 

comets, 334. 
Bredechin on tails of comets, 78. 
British Association on meteoric 

dust, 11. 
Brodie, B., on constitution of 

matter, 49, 54. 
Bruno, Giordano, cited, 496, 553. 
Buckingham on crater Linne, 

392. 
Buffon cited, 339 ; hypothesis of, 

611. 
Burnham, S. W., on double stars, 

512, 513. 
Byi'gius crater, 390. 



Callawav, C, on primitive tides, 
265. 

Calvert on meteoric dust, 13. 

Campanella cited, 553. 

Capellar phase, 541. 

Carnelly, T. on water under pres- 
sure, 270. 

Carpenter, W. B., on area of 
ocean, 466. 

Cassini on zodiacal light, 24; on 
Mercury, 423; on Saturn's 
rings, 582. 

Central solidification, 220. 

Centrifugal force in ring making, 
110, 115; in tides, 129; in ar- 



IlfDEX. 



625 



rangement of heavier matters, 
137. 

Centripetal influence in tides, 
129; in arrangement of heavier 
matters, 137. 

Chandler, S., on comet of 1882 h, 
31. 

Chaotic stage, 539, 618, 619. 

Chemical reactions on primeval 
planets, 274, 327. 

Childrey on zodiacal light, 26 

Chladni on meteors, 13, 16. 

Clark, Alvan, on companion of 
Sirius, 434. 

Clarke, F. W., on constitution of 
matter, 49, 56. 

Clausius, li., on freezing under 
pressure, 27; on reconcentra- 
tion of energv, 493. 

Clefts on moon', 391. 

Climates, deterioration of, 485; 
cause of, 486. 

Climatic forces, in early times, 
269 ; resulting from astronomi- 
cal changes, 278-90; affected 
by increased obliquity, 283 ; by 
motion of apsides, 285; by 
changes in eccentricity, 298. 

Clissold on Swedenborg,' 566. 

Cloudiness on Venus, 422; on 
Mercury^ 424; on Jupiter, 433, 
434, 435 ; on ultra-Jovian plan- 
ets, 447. 

Clouds, first formation of, 272. 

Clusters of stars, 47, 48 ; in Her- 
cules, 118. 

Coagulating nebula, 105. 

Collision of worlds, 478, 516, 518. 

Colonies in palaeontology , 281. 

Colors of stars, 522 seq., 528. 

Comet of 1881, 29. 

Comet of 1882 h, 30, disintegra- 
tion of, 31. 

Comets, motions and phenomena 
of, 27; of short period, 28; 
tenuity of, 32, 184; disinteg?-a- 
tion of, 31, 32, 75, 206, 482; 
connected witli meteoric show- 
ers, 32, 33, 34, 75; physical 
condition of, 34, 40; tails of, as 
viewed by Newton, 51* evolu- 
40 



j tion of, 73; determination of 
' orbits of, 73-4; influenced by 
planets, 74; light of, 77; tails 
of, 77-8; as strangers in our 
system, 182, 196, 610, 615; di- 
rection of motion of, 182; con- 
trolled by same laws as planets, 
183; origin of on Faye's the- 
ory, 205, 211. 

Common, A. on comet of 1882 h, 31. 

Comparative geology, the keys of, 
534. 

Composition of fixed stars, 191. 
i Conception, final, of orogenic 
history, 326-31. 

Conceptions respecting mountain 
making, 323. 

Conspectus of views on matter in 
space, 65 ; on orogenic specula- 
tions, 331. 

Continental trends, 352. 

Contractional theory in orog- 
raphy, 294-314, 324; inade- 
quacy of, 314, 

Contraction as a source of heat, 
81-7 ; as cause of acceleration, 
459. 

Cooling of planets, 458.. 

Cooling planet, conditions on, 215. 

Ceoling through descent of rains, 
273 ; impeded by crust, 275. 

Cope on habitability, 498. 

Copernicus crater, 387; radial 
streaks of, 390, 404. 

Cornelius, C. S., on nebular evo- 
lution, 120. 

Cosmical dust, examples of, 3; 
citations on, 11 ; quantity of, 13 ; 
general view on, 48; sundry 
opinions on, 49-65; aggrega- 
tion of, 66, 71 ; resisting action 
of, 69-71; primordiality of, 
539. See also " matter of 
space." 

Cosmical speculation, 65. 

Cosmic history generalized, 621, 

Cosmic period"^s, 215, 216, 450; on 
moon, 380; on Mars, 415; on 
Jupiter, 429; on Jovian satel- 
lites, 438 ; on ultra-Jovian plan- 
ets, 445. 



626 



Iiq-DEX. 



Cosmic tides influencing rotation, 
129. 

Cosmogony. See " Nebulae," 
" Cosmical dust," "Tides," etc. 

Craters, lunar, 386, 390; Coper- 
nicus, 387; Theophilus, map of, 
388: Tvcho, 389; Kepler and 
others, 390; floors of, 408. 

Croll, J., on nebular heat, 93, 207: 
on age of the sun, 179; on cli- 
matic effect of precession, 288 ; 
on influence of eccentricity, 
289 ; on change of axis, 334 ; on 
geological time, 368, 373; on 
continental erosion, 373, 374. 

Crookes, W., on radiant matter, 
49. 77. 

Cruls on comet of 1882 b, 30. 

Crushing influence of tides, 131, 
255, 347. 

Crushing, thermal effects of, 131, 
255, 346, 347. 

Crust, incipient, 218 : slipping of, 
220, 308-9 ; transformations of, 
274-8; fire-formed, 274; influ- 
ence of in cooling, 275; sink- 
ing as formed, 307; subsidence 
of, 314-9 ; unequal thickness of, 
335 ; thicker under the oceans, 
337; on moon, 402: of ice, 442. 
446. 

Currents on the surface of a neb- 
ula, 130. 

Cusanus cited, 552. 

Cutting. H. A., on rock absorp- 
tion, 462. 

Cuvier, G., on Leibnitz, 558. 

Cycle, cosmic, 534-48, 621 ; reflec- 
tions on, 544. 

Cycles of matter, 495. 

D 

Dana, J. D.. on influence of 
ocean in wrinkling, 301; on 
mountain making, 302, 303; on 
subsidence of crust, 316; on 
synclinorium, 322; on trends in 
Pacific, 352; on time ratios, 
358, 364. 

Darwin, C, on age of the earth, 
180. 



Darwin, G. H., cited, 581; on 
retral sliding of tide, 235; on 
submeridionality, 255 ; memoirs 
by, 258; on primitive tides, 
265; on velocity of wind, 269; 
on terrestrial cooling, 296; on 
change of axis, 334 ; on earth's 
rigidity, 343. 

Daubenev on mountain making, 
293 ; oil earth's interior, 339. 

Daubree on meteoric dust, 8, 11. 

Daw, H., on mountain making, 
293, 332: on the earth's interi- 
or, 339. 

Dawson, J. W., on slipping of 
crust, 309. 

Decay, planetary, 451; according 
to Kant, 585. 

Deep-sea temperature, 337. 

Deformative tide, 226; crushing 
influence of, 255. 

Delambre, cited, 551, 

Delaunay on terrestrial rigidity, 
341; on tidal retardation, 474. 

Delesse on rock absorption, 464. 

Delta of Mississippi River. 372, 
453. 

Democritus cited, 553. 

Denning, W,, on meteorites. 13. 

Densities of Jovian satellites, 
440; of planets, 579. 

Densities of outer planets alleged 
too low, 177. 

Density of Saturn. 443; Uranus 
and Neptune, 443; Jovian sat- 
ellites, 440. 

Density of atmosphere, effects of 
low, '271. 

Density of solar nebula, 161-4, 
421, 424, 589; fallacy concern- 
iug, 178; influence of on or- 
bital velocity, 161 : alleged too 
low, 184. 

Density under mountains. 322, 
330.' 

Deposition and time, 369. 

Derham, W., cited, 496. 

Descartes on a wrinkling crust, 
295; on earth's interior, 339; 
vortical theory of, 554. 

Deschanel cited, 412. 



INDEX. 



627 



Desiccation of continents, 471. 

Desor, E., on Niagara gorge, 809. 

Deville on dissociation of matter, 
48; on rock absorption, 464, 

Dewar on Lockyer's views, 49. 

Direct -rotation, how resulting, 
123-4. 

Direction of rotation in resulting 
spheroid, 122-9; what it de- 
pends on, 123; how estimated 
by Faye, 203. 

Discoid ring, 111-2. 

Discordant tides, 239; action of 
on rotation, 398, 404. 

Disintegration of comets, 31, 32, 
75, 206, 482; of Saturn's rings, 
483. 

Disruption of a nebular ring, 119, 
208. 

Dissipation of energy, 489. 

Dissociation of matter, opinions 
on, 48; in space, 59; in the 
sun, 59; in nebulae, 193. 

Distances of planets in Faye's 
theory, 205. 

Distortion from tides, 439. 

Divination, scientific, 535. 

Doberck, W., on comet of 1882 
h, 30. 

Donati's comet, 47. 

Doolittle, M. H., on resisting 
matter in space, 70. 

Downthrow of strata, 304. 

Draper, J. W., on red heat, 272; 
on spectrum of Orion nebula, 
531. 

Drayson on glaciation, 285, 290. 

Dufour on meteoric matter, 14. 

Dumas on dissociation of matter, 
48. 

Duncan, P. M., on solar heat, 56. 

Du Prel on discoid ring, 112. 

Durocher on rock absorption, 461. 

Dust falls, 6. 

Dust of time, 3. 

Dust, organic, 6. 7. 

Dust, volcanic, 7. 

Dutton, C. E., on contractional 
theory, 304-7; on internal tem- 
peratures, 306; on slipping of 
crust, 308. 



Dykes on moon, 403. 
Dynamical theory of tides, 225. 

E 

Earth, tidal influence of, 248; 
planetologically viewed, 338 
seq. ; former high temperature 
of, 339; present interior of, 
339 ; rigidity of, 340 ; meridion- 
al trends on, 350; age of. 355; 
a former sun, 380. 

Earthquakes connected with 
moon, 348. 

Eastman, J. R., on meteors, 5. 

Eccentricity of planetary orbits, 
174; climatic influence of, 288- 
90; Kant's theory of, 580. 

Ehrenl)erg on meteoric dust, 6. 
13. 

Elastic forces in a contracting 
body, 84. 

Electricitv on primeval planet, 
273. 

Elemental atoms, 49. 

Elements, compound nature of, 
48. _ _ 

Elevation without plication, 304. 

Elliptic orbit, how caused, 67, 74, 
174, 554, 556, 564, 576, 615. 

Elliptic orbits alleged unexplain- 
ed, 173. 

Empedocles on love and hate, 553. 

Encke's comet resisted, 479. 

Endlich, F. M., on explosive phe- 
nomena, 339; on desiccation, 
471. 

Ennis, J., on spiral nebulje, 99; 
on rotation of nebulae, 165; 
cited, 339. 

Eozoic tides, 265. 

Epicurus cited, 553. 

Equal areas, law of, 106, 613 ; in^ 
fluence of in direction of rota- 
tion, 124. 

Equatorial lands more or less 
emergent, 278. 

Equilibrium, final, in nature, 488 
seq. 

Equilibrium theory of tides, 225. 

Equinoxes, motion of, 285. 

Eroded condition of planets, 451. 



628 



IXDEX. 



Erosion along anticUnals, 335. 

Erosion, amount of, 451; at Ni- 
agara gorge, 8G9, 878, 452; in 
remote times, 452; of Missis- 
sippi, 372, 378, 453; on Mercury 
and Venus, 457; on moon, 457: 
on Mars, 458 ; on Jovian satel- 
lites, 458. 

Erosion and time, 369, 374. 

Erosion limited on moon, 412. 

Erosive action, of tides. 268: of 
lava torrents, 399. 

Eruption on temporary star, 517. 

Eruptive phase, 543. 

Eta Argus, changes on, 88. 

Ether, Xewton's views on, 50-2; 
influence of, 479. 

Evolution, tidal. See "Tides," 
etc. 

F 

Falcate forms of nebula, 102-3. 

Fan action about the sun, 59, 60. 

Fan structure in the Alps. 808, 
809. 

Faunal changes and astronomical 
conditions, 281. 284. 

Favre, A., on a wrinkling crust. 
297. 

Faye, on Siemens' solar theory. 
61; on tails of comets, 78; on 
direction of rotation, 128; on 
retrograde motions. 153, 158; 
on periodic time of Phobos, 168 : 
on comets belonging to our 
system, 182; on improbability 
of annulation. 187; this opin- 
ion examined, 189-90; on a 
modified form of nebular theorv 
198-207; criticisms of. 207-14: 
on subsidence of ocean's bot- 
tom, 317, 328. 832; on geal 
tide on moon, 884; on lunar 
geology, 407; on lunar fluids, 
471 ; on solar spots, 520. 

Ferrel. W., on tides. 225. 

Film tide, 227. 

Final causes, 608. 

Finiteness of the world. 491, 505. 

Finlay, on comet of 1882 h, 30. 

Fire-formed crust, 274; disap- 
pearance of, 277. 



I Fire-mist stage of a planet. 217; 

I of the stars, 526, 530, 532; of 

j nebula?. 540. 

Firmamental organization. 574, 

i 598, 602, 605. 

I Fisher, 0., cited, 347; oil earth 
oscillation, 260; on terrestrial 
cooling. 296 ; on radial contrac- 
tion, 803; on contractional 
theory. 306; on terrestrial 
physics, 306 : on internal vapors, 
311 ; on mashing together, 821 ; 
on roots of mountains, 321 ; on 
orogeny, 334; on origin of 
ocean's basin, 835 ; on internal 
soliditv, 341: on earth's age. 
356. 

Fisk, J., corrected. 503. 

Fixed stars, in motion. 141, 575 : 
alleged not uniform in compo- 
sition, 191. 

Flammarion on habitability, 496. 

Flight, W., on meteoric occlu- 
sions, 58. 

Floating mineral matters, 218. 

Flood, cause of, 583. 

Flow on surface of nebula, 180. 
i Fluctuation, total, of a tide, 
226-7. 

Fluids on moon, 402, 407. 
j Folds of crust. See " Wrinkles.*' 
! Forbes, D.. on Mallet's theorv, 
I 319. 

j Forbes. President, on habitabil- 
I ity, 497. 

I Forces of nature, magnitude of, 
223. 

Forms of nebula changing, 87-94 ; 
causes of. 99-104 

Formula for law of angular ve- 
locity, 109; linear velocity, 110: 
width of nebulur ring, 116; di- 
i rection of rotation, 126; law of 
densitv in the solar nebula 
(Faye), 128, 189, 204; constancy 
of differential centrifugal ten- 
dency, 138; equal differential 
centrifugal and centripetal ten- 
dencies. 139 ; relations of peri- 
odic times. 159, 167; periodic 
time n times as great, 169; con- 



INDEX. 



629 



ditions of no annulation, 188; 
relation of contraction to annu- 
lating velocity', 100; tenuity of 
solar nebula, 200; orbital 
motion in a hollow sphere, 202; 
relative length of planetary 
periods, 216; efliciency of tidal 
forcej 228; linear height of 
tide at any point, 228; linear 
height on homogeneous sphe- 
roid, 229 ; linear height on the 
earth, 229; zero tide, 229; tide 
on one planet in terms of tide 
on another, 229; retardative 
component of tidal force, 233; 
equatorial centrifugal force on 
the earth, 257 ; erosive efficiency 
of tides, 2G8; earth's heat as a 
sun, 380; absorption of water, 
382; absorption of water and 
air, 383; geal tide on moon, 
384; density of atmosphere on 
a planet, 411; determination of 
altitude by barometer, 411; 
temperature of boiling point, 
412; height of tide on any 
planet, with any tide-mover, 
418 ; centrifugal force in terms 
of same on another planet, 
426 ; intensity of gravity in geal 
terms, 426 ; various Jovian rela- 
tions to earth, 427-8 ; height of 
homogeneous atmosphere on 
any planet, 430; height of earth's 
homogeneous atmosphere, 
430-1 ; moment of inertia of a 
sphere, 437; final levelling of 
land, 456; indices of rock ab- 
sorption, 463-4; specific gravity 
of rocks, 463-4; atmospheric 
pressure in a deep shaft, 469. 

Fourier on a problem in thermics, 
305. 

Fragmental deposits in moun- 
tains, 318. 

Frankland on porosity of moon, 
465; on heat of Orion nebula, 
532. 

Freezing point under pressure, 
270. 

Friction in nebular matter, 100, 



122, 124, 127, 165; in tides, 
233, 250. See "Tides." 

Frisby, E., on comet of 1882 b, 
31. 

Furrows the counterpart of wrin- 
kles, 300. 

G 

Gardner. J. S., on subsidence of 
crust, 316, 334. 

Gardner, J. T., on Niagara gorge, 
370. 

Gases in mountain making, 292. 

Gassendi cited, 553. 

Gautier on nebulfe, 42, 88, 92. 

Geal tides on moon, 248, 396 seq. 

Geanticlinals, 327. 

Geikie, A., on continental ero- 
sion, 373. 

Geognostic regions, 357. 

Geologv, pure, 536 : comparative, 
536-7. 

Geosynclinals, deposition along, 
314; uplift of, 318. 

Gilbert, G. K., on lacolitic moun- 
tains, 294. 

Gilmore, Q. A., on rock absorp- 
tion, 462. 

Glacial periods and time, 368. 

Gordon-Gumming, Miss C. F., on 
floating lava, 218. 

Gorge of Niagara, 369 seq. ; of St. 
Anthony, 372, 378. 

Gravity on moon, 400-1 ; on Mars, 
415 ; on Jupiter, 426. 

Green on internal vapors, 311. 

Gregory on Kepler, 554; on Des- 
cartes, 555. 

Grenfel, J. G., on primitive tides, 
265. 

Groom bridge 1830, motion of, 92. 

Grove, W. R,., on matter in'space, 
52. 

Gruithuisen on moon, 385. 

Guppy, H. B., on river sediments, 
373. 

Gyration, radius of, in planets, 
162, 437. 

H 

Haanel, E., on constitution of 
elements, 48. 



630 



IlfDEX. 



Habitability of other worlds, 496; 
absolutely viewed, 497-500; 
viewed from human standard, 
500; restricted limits of, 507; 
Kant on, 591. 

Hall, J., on distribution of faunas, 
281; on central heat, 295; on 
sedimentation along geosyneli- 
nals, 314; on orogeny, 333; on 
Niagara gorge, 369. 

Hall, James (of Edinburgh), on a 
wrinkling crust, 295. 

Hall, Maxwell, on solar heat, 61. 

Halley on meteors, 16. 

Hannay, J. B., on water under 
pressure, 270. 

Harmonic circulation. 564. 

Haughton, S., on primitive tides. 
265; on change of axis, 334. 
580 ; on time ratios, 359 ; on 
geological duration, 366; on 
area of ocean, 466; cited, 341. 

Hayden, F. V., on desiccation, 471. 

Heat resulting from contraction, 
81-7; from tidal crushing, 256; 
from contractional crushing, 
319-23 ; in the stars, 526. 

Heavier matters, how arranged, 
137. 

Heim. A., on contractional theo- 
ry, 312. 

Helmholtz on matter in space, 52 ; 
on solar heat, 81; on nebular 
rotation, 94; on age of the sun, 
179; on dissipation of energy, 
489 ; on vortex ring, 569. 

Helvetius on lunar surface, 385. 

Hennessey, H. G., cited, 341. 

Heraclides cited, 551. 

Hercules, cluster in, 118; solar 
motion toward, 141, 202. 

Herschel, A. S., on the constitu- 
tion of matter, 61, 533. j 

Herschel, J., on Orion nebula, : 
105; on isothermal lines in 



crust, 275 : 



astronomical 



causes of climate, 290; on a 
plastic zone, 315; on lunar cra- 
ters, 387 ; on ratio of land and 
water, 466; on mass of atmos- 
phere, 468: on nebulae, 598, 605. 



Herschel, W., on nebulae, 35, 41; 
on Magellanic Clouds, 88; on 
orders of nebulae, 140 ; on Mar- 
tial ice caps, 4l6; on habita- 
bility of sun, 497 ; on structure 
of the heavens, 598 ; cited, 146 ; 
511. 

Hicetas on rotation of earth, 551. 

Hilgard, E. W., cited, 372; on 
crushing effects, 347. 

Hilgard, J. E., on Gulf of Mexi- 
co, 453. 

Hinrichs, G., on dissociation of 
matter, 48; on spiral nebulae, 
10 1; on direction of rotation, 
127; on planetary velocities, 
159; on planetary intervals. 
173. 

Hire, de la, cited, 575. 

Hirn, A., on Siemens' theory, 63, 
64; on Saturn's rings, 483. 

Hirsch on geological climates, 
290. 

Hitchcock, C. H., on pressure 
from continental side, 309; on 
mashing together, 323 ; on mol- 
ten origin of granites, 517. 

Holden, E. S., on changes in 
nebulae, 88. 

Homogeneous atmosphere, 430. 

Hopkins, W., on floating rock 
masses, 218, 272; on a wrink- 
ling crust, 296 ; on local lakes 
of lava, 332; on internal li- 
quidity, 340, 346. 

Horizontal component of tidal 
force, 232, 351. 

Hough, G. W., on Jupiter, 429. 

Huggins, W., on nebular spectra, 
47; on cometary spectra, 58; 
on motion of nebulae, 91; on 
crater Linne, 392; on tempo- 
rary star, 514; on spectrum of 
Orion nebula, 531. 

Humboldt, A., cited, 5; on zodi- 
acal light, 23, 24 ; on matter in 
space, 53; on temporary stars, 
514; on Laplace, 606. 

Humphreys and Abbott on Mis- 
sissippi River, 372. 

Hunt, T. S., on the matter of 



INDEX. 



631 



space, 49, 54 ; on moon's atmos- 
phere, 57; on primeval chemis- 
try, 274; on aplastic zone, 315; 
on orogeny, 333; on rock ab- 
sorption, 4G1. 

Hutton, P. W., on Mallet^s 
theory, 319. 

Huxley, T. H., on age of the 
earth, 180. 

Huvgens cited, 496; on nebulte, 
575. 

Hyginus crater, changes near, 
393, 395. 

Hyperbolic orbit, how caused, 
*74. 

Hypothesis ripening to doctrine, 
153. 



Ice caps of Mars, 416. 

Ice-covered planets, 446; satel- 
lites, 442. 

Ice periods, 290. 

Igneous theory of Leibnitz, 559 
seq. 

Implications excluded from nebu- 
lar theory, 196-8. 

Inclinations in planetary systems, 
129, 171, 172, 621 ; of Uranian 
and Neptunian, 153; how ex- 
plained, 154 seq. ; of axis in- 
creased by lagging tide, 243; 
sometimes diminished, 244. 

Incrustation on moon, 397. 

Incrustive phase, 542. 

Index of rock absorption, 460. 

Infinitude of worlds, 585. 

Initial temperature of earth, 307. 

Intelligence on other worlds, 502, 
592. 

Internal tides, action of, 398. 

Intervals between orbits, 173. 

Invariable plane of solar system, 
172. 

Iron, magnetic, in meteoric dust, 
10. 

Iron floating on molten iron, 218, 
219. 

Isothermal lines in crust, 275; 
ascent of, 276, 324. 



Janssen on matter around the 
sun, 64. 

Jones, G., on zodiacal light, 23, 
25. 

Jovian phase, 543. See "Jupi- 
ter." 

Julien, C-F., on effect of preces- 
sion, 288. 

Jupiter, condition of, 149-; satel- 
lites of, 150; tidal influence of, 
248; why having several satel- 
lites, 262 ; physical relations of, 
425; compared with earth, 427; 
trade winds on, 428; cosmic 
periods of, 429 ; physical condi- 
tion of, 430, 441, 543; atmos- 

* phere of, 430-1 ; luminosity of, 
432; tides on, 433, 434-7; tides 
on satellites of, 438; densities 
of satellites of, 440; habita- 
bility of, 505 ; in Kant's theory, 
581.' 

K 

Kant on comets, 27, 576; on or- 
ders of nebulae, 140, 575; on 
retardative action of tides, 249, 
473, 580 ; on restoration of the 
cosmos, 492, 586; on habita- 
bility, 496 ; general cosmogony 
of, 574. 

Keferstein on a plastic zone, 315; 
on plications, 332. 

Kepler crater, radial streaks of, 
390, 404. 

Kepler, third law of, 159 ; cosmic 
theory of, 553. 

Kilauea, 218. 

King, C, on downthrows, 304; 
on elevation and subsidence, 
317; on Triassic, 362. 

Kirkwood, D., on meteoric dust, 
11; on spiral nebulae, 99; on 
discoid ring, 112; on direction 
of rotation, 127; on density of 
solar nebula, 163 ; on masses of 
Mars and Asteroids, 176; on 
comets as members of solar sys- 
tem, 181. 



632 



IXDEX. 



Klein, H. J., on crater Hyginus 
N". 393-4; on lunar craters, 
408. 

Konig, C, cited, 485. 

Kretz, on ether, 479. 

Kreutz on comet of 1882 h, 31. 

Kriimmel on altitudes of conti- 
nents, 454. 

Krusenstern on a fire ball. 5. 



Lacolitic mountains, 294. 

Lagging of tide, 231 ; retards ro- 
tation, 232, 396; causes reces- 
sion of tide-producer, 239; 
greater in nucleus, 239; in- 
creases inclination of axis, 243 ; 
retards moon's rotation, 249, 
396 seq. ; when discordant, 398. 

Lake survey on Niagara gorge. 
371. 

Lambert, J. H.. on cosmogony, 
597. 

Lancetta on dust falls, 11. 

Lane, H.^ on solar heat, 83; on 
central density of sun, 162. 

Langiey, S. P., on absorbent me- 
dia in space, 61, 64, 381 ; con- 
sequences of, 413. 

Laplace on zodiacal light, 24; on 
rotation of resulting mass, 121, 
614; on comets as strangers in 
our system, 182, 610, 615; on 
annulation, 187, 613; on tides, 
225; on change of axis, 334; on 
tidal retardation, 474; on sta- 
bility of system, 478 ; on habi- 
tability, 496, 606; on the sys- 
tem of the world, 606-17; criti- 
cism of, on Newton, 607; con- 
fidence of, in his hypothesis, 
610; on lunar synchronism, 
616. 

Lardner on habitability^ 496. 

Larkin, E. L., on forces of na- 
ture, 223. 

Lasell on Omega nebula, 89. 

Laurentian tides, 266. 

Laya ejections on moon. 399. 403, 
408-9. 



Lava floating, 218. 

Lava floes on incrusting planets, 
397. 

Lava floods. 517: on moon, 399, 
403. 

Leibnitz on earth's interior, 339, 
558-63 ; on atoms, 553 ; on cos- 
mogony, 558; on monads, 571. 

Leipoldt on heights of continents, 
454. 

Lenz on meteoric dust, 9. 

Leonids, 21. 

Le Sage cited, 620. 

Lescarbault on A^ulcan, 215. 

Lesley, J. P., on downthrows, 
304. 

Leueippus cited, 553. 

Levelling of land, 454. 

Leverrier on Tempel's comet, 33. 

Lewis, H. C. on geological time, 
378. 

Liais on zodiacal light, 24. 

Librations, 132. 

Lichtenberg, Hofrath, cited, 582. 

Lichtenstein on meteors, 16. 

Light, wave lengths of, 37; 
evolved in collisions of cosmic 
atoms, 73; of comets, how 
caused, 77. 

Linne crater, 392, 395. 

Liquefaction of water, 270. 

Liquefaction from diminished 
pressure, 221. 

Liquid matter forming on a 
planet, 217. 

Liquid nucleus, 340. 

Liveing on Lockyer's theory, 49 ; 
on Siemens' theory, 57. 

Lockyer, J. N., on compound na- 
ture of elements, 48, 56; on 
heat of Orion nebula, 532. 

Lodge, 0., on ethereal origin of 
matter, 49; on-' water under 
pressure, 270. 

Logan, W., on Eozoic, 359. 

Lohrman on moon, 385, 392. 

Loomis, E., on Martial climate, 
417. 

Lovering, J., on phosphorescence, 
5. 

Lucretius cited, 553. 591. 



IKDEX. 



633 



Luminosities of planets, 432. 

Lunar phase, 544. 

Lunar tide, 248; in primitive 

times, 258; influence of in 

mountain making, 326. See 

"Tides." 
Lvell, C, on age of the earth, 

'180; on crushing of strata, 322; 

on time ratios, 368 ; on Niagara 

gorge, 369. 

M 

Macvicar, J. G., on constitution 
of matter, 49. 

Maedler on firmamental rotation, 
140; on crater Linne, 392. 

Magellanic clouds, 42; changes 
in, 88. 

Mallet, J. W., on solidifying iron, 
218 ; on unequal radial shrink- 
age, 303 ; on mashing of strata, 
319; on orogeny, 334; on heat 
from crushing, 346. 

Man's position among intelli- 
gences, 592. 

Marcou, J., on Niagara gorge, 
369. 

Marine tides in early times, 256. 

Mars, satellite of, with period too 
short, 168 ; axial retardation of, 
250 ; why having two satellites, 
262; phenomena of, 415; age 
of, 415 ; tidal influences on, 417 ; 
atmosphere of, 419; boiling 
water on, 409 ; habitability of, 
503. 

Marsh, G. P., on floating lava, 
218. 

Martial phase, 544. 

Martins, C, on astronomical cli- 
mates, 290. 

Marx on meteoric dust, 9. 

Mashing together in orogeny, 302, 
319-23, 324. 

Matter, finite existence of, 546, 
584. 

Matter, of space, opinions on, 49, 
200 ; tabular conspectus of, 65 ; 
aggregation of, 66 ; as a resist- 
ing medium, 104, 169, 478-81. 



Maundeville, Sir John, on form 

of earth, 552. 
Maupertuis cited, 553, 575. 
Maximum internal temperature, 

221. 
Maxwell on plurality of worlds, 

497. 
Maxwell, C, cited, 412, 493; on 

Saturn's rings, 121, 179, 582; 

on terrestrial cooling, 296. 
McGee, J. W., on ice periods, 

290. 
Mechanical constitution of the 

world, 589; not atheistic, 591. 
Mercury, tides on, 250, 424, 476; 

why having no satellite, 262; 

planetography of, 423; condi- 
tions on, 424; erosion on, 457; 

habitability of, 500. 
Meridional trends, 252-4, 325; 

strictly submeridional, 254; in 

the earth, 350; primitive in 

origin, 353. 
Messier craters, 393, 395. 
Metamorphism of rocks, 276, 315; 

in mountain making, 331. 
Meteoric dust. See " Cosmical 

dust." 
Meteoric streak, 5 ; stones, 15. 
Meteoroidal resistance, 70, 480. 
Meteoroidal swarms, 17 seq., 75, 

482; table of, 21; number of, 

22. 
Meteors, 3, trains of, 5; number 

of, 13, 22; height of, 15; ve- 
locity of, 16; Von Reichenbach 

on, 75-6. 
Milky Way, T. Wright on, 572; 

Kant on, 574, 583, 586; central 

body of, 589; Lambert on, 598; 

W. Herschel on, 598; Laplace 

on, 609. 
Mill, J. S., on nebular theory, 

153. 
Miller, W., on habitabilitv, 497. 
Mitchel on Pleiades, 612. ' 
Mitchell, Maria, on meteors, 5. 
Molecule, permanence of, 547. 
Molten matter, outflowing tidal- 

ly, 265, 399; sources of, 344; 

zone of, 344; outflows of on 



634 



IN^DEX. 



earth, 401 ; on temporary stars, 
517, 543. 

Molten nucleus, theory of, 294, 
340. 

Molten phase, 217, 542. 

Momentum, angular, oX rotation, 
109. 

Monads, 571. 

Mont Blanc, section across, 308. 

Moon, atmosphere of, absorbed, 
57, 382; tides on, 248; retarda- 
tion of, on axis, 249 ; disappear- 
ance of water on, 251; origi- 
nating from disruption of 
earth, 259; influence of in 
mountain making, 326; planet- 
ogenic history of, 379 seq. ; 
planetary relations of, 379; age 
of, 380 ; early condition of, 381 ; 
atmosphere of wanting, 381 ; 
physical aspects of, 385; map 
of, 386; craters on, 386 seq. ; 
radial streaks on, 390 ; furrows 
or clefts on, 391 ; changes on, 
392-5, 414; tidal evolution of, 
395; retarded rotation of, 396 
seq.; incrustation of, 397; ero- 
sion on, 457; synchronism of, 
404, 557, 580, 616; habitability 
of, 502. 

Morande, Rey de, on colder cli- 
mates, 487.' 

Morris, C, on Siemens' theory, 
57; on habitability, 498; on 
matter in space, 61. 

Morrison on comet of 1882 h, 31. 

Mountain crests thinned, 335. 

Mountain making, 291-335; sep- 
arate conceptions on, 323-7; 
Leibnitz on, 562; aeriform 
agents in, 292. 

Mountains of elevation, 291; of 
relief, 291. 

Mountain forms in cooling iron, 
219. 

Mousson on freezing under pres- 
sure, 271. 

Murphy, J. J., on effect of pre- 
cession, 288; on eccentricitv, 
290. 

Murray on meteoric dust, 11. 



N 

Nasmyth on moon, 385, 621. 

Nebulae, 35-48, 80-142; physical 
condition of, 40; forms of, 42, 
99, 117, 601, 604, 605; spectra 
of, 42-8, 192, 531; evolution 
of, 73, 105; heat of from re- 
frigerative contraction, 81 ; 
heat of from aggregation, 92- 
4; changes of form in, 87-94; 
rotation of, 94-106; approach 
of, 95; spiral forms of, 99-102; 
sickle forms of, 102-3; evolu- 
tion of without rotation, 105, 
118; local nuclei in, 106, 118; 
annulation of, 106-19; non-an- 
nvdating, 105, 118; spheration 
of ring from, 119-42; influ- 
enced by cosmic tides, 129; 
currents on, 130 ; orders of, 139 ; 
distinction of firmamental and 
solar, 146; cosmogonic condi- 
tions of, 531 ; formation of, 66, 
533; Herschel on, 599, 601-4; 
Laplace on, 606. 

Nebular stage, 540. 

Nebular theory verified by facts, 
147; presumptions sustaining, 
151; indictments against, 152, 
198 ; supported by great names, 
153 ; objections to, 153-95 ; does 
not assume complete continu- 
ity of primitive matter, 185; 
does not imply an absolute be- 
ginning, 196; nor explain ori- 
gins, 196; nor exclude plan 
and purpose, 197; as modified 
by Faye, 198-212; as modified 
by Spiiler, 212-4. 

Neison on moon, 385; on crater 
Linne, 393; on Hyginus N., 
394. 

Nelson on comet of 1882 &, 31. 

Neptune, apsides of, 285; habit- 
ability of, 499, 506. 

Neptunian system retrograde, 153, 
157. 

Newberry, J. S., on primitive 
tides, 265. 

Newcomb, S., on dense clusters 



INDEX. 



635 



of stars, 48 ; on solar heat, 83 ; 
on discoid ring, 112; on inter- 
vals between orbits, 173; on 
age of the sun, 179, 350; on 
terrestrial rigidity, 341 ; on 
solar spots, 520; cited, 425, 601. 

Newton, H. A., on meteors, 7. 

Newton, Sir I., on an interplan- 
etary medium, 50, 479; on 
planetary orbits, 172; on tides, 
225; on divine agency, 007; 
cited, 339. 

Niagara, gorge of, 369, 378, 452. 

Niesten on comets, 27. 

Nilotic delta, 372. 

Nordenskjold on meteoric dust, 
8. 

Norton, W. A., on comets, 78. 

Novemlaer meteoric shower, 14, 
17 seq., 33. 

Nucleated phase, 541. 

Nucleating phase, 540. 

Nucleus of planet in liquid stage, 
217; becoming solid, 220, 323. 

Nucleus of stars. 520, 

Nutations, 132, 010. 

o 

Objections often trivial, 194; 
from planetary motions, 153- 
70; from planetary positions, 
171-5; from planetary masses 
and densities, 175-9; from ter- 
restrial duration, 179-81 ; from 
comets, stars and nebulaB, 181- 
0; of an anonymous writer, 
194. 

Oblateness varying with rotation, 
278. 

Obliquity of axis, effects of, 282-5. 
See "Inclinations." 

Ocean, birth of, 273 ; influence of 
in mountain making, 301. 325, 
329, 331 ; basin of, how formed, 
335 ; volume of, 400 ; depth of, 
466; bottom configuration of, 
302. 

Oceanic trends, 352. 

Olbers' crater, 390. 

01 bars on origin of asteroids, 177. 



Old age of planets, 451. 

Olmstead, 1)., on meteors, 16; on 
zodiacal light, 23, 26. 

Omega nebula, changes in, 88, 
89, 90. 

Oppolzer on origin of meteors, 33. 

Orbital motion, retardation of, 
281. 

Orbital movements, of three 
bodies in space, 66, 95; when 
attraction varies with the dis- 
tance, 202. 

Orbits, of meteoric swarms, 17 
seq. ; of comets, how determin- 
ed, 73-4; of satellites, how in- 
verted, 155; how inclined, 171. 

Orbits assumed described in prim- 
itive nebula, 201. 

Orders of nebuhe, 139. 

Orion, nebula in, 42, 45; changes 
of form of, 88, 611; curdling 
Huygenian region in, 105; 
spectrum of, 531; stars in, 
525. 

Orogenic forces, 291-335, 326. 

Orogenic history, final conception 
of, 326-35, 334; conspectus of 
views on, 332. 

Oscillation on an axis, 132; of 
earth, 260; of levels, 280. 

Overturn of a system, 154-5. 



Palaeozoic tides, 263. 

Parabolic orbit, how caused, 74. 

Parsons, S., on meteoric resist- 
ances in space, 70; on periodic 
times, 167; on rotary motion, 
170; on age of the earth, 179, 
180 ; on comets as an objection, 
181; on tenuity of primitive 
nebula, 184; on improbability 
of annulation, 186; against 
nebular theory, 198. 

Peirce, B., on rings of Saturn, 35, 
582; on solar heat, 81; on in- 
tra- Jovian ring, 177. 

Periodic times alleged too long, 
158; alleged too short, 167. 

Periods, geological, 365. 



636 



INDEX. 



Perrey, A., on earthquakes, 348. 

Perseids, 21. 

Pfaff, F. on mountain making, 
312. 

Phases of star life, 529, 541 ; of 
planet life, 543. 

Phobos, periodic time of loo short, 
168; tidal action of, 418; fall- 
ing to Mars, 481. 

Photospheric matter, 527 seq., 
541 seq. 

Pickering, E. C, on variable 
stars. 

Pilar, G., on the ice age, 290. 

Plan not excluded, 197. 

Planetary nebulse, 46. 

Planetogenic constants, table of, 
449; remarks on, 450. 

Planet ogeny of Leibnitz, 564; of 
Kant, 577. 

Planets of other systems, 512. 

Plastic zone, 313, 315, 323, 325. 

Plicated strata beneath unpli- 
cated, 301. 

Plications, 301, 304; not always 
accompanying elevation, 304; 
localization of, 305: amount of. 
318. See "Wrinkles." 

Pliny cited, 552. 

Plummeron nebular spectra. 192. 

Plutarch cited, 385. 

Plutonic theory, 563. 

Poisson on meteors, 16; on tem- 
perature of space, 199, 208. 

Polar lands affected bv rotation, 
280. 

Polar snows affected by inclina- 
tion of axis, 284; by precession, 
287; bv changes in eccentricitv, 
289. 

Powell, J. W., on downthrows, 
304. 

Pratt, Archdeacon, on unequal 
radial shrinkage, 303; on dens- 
ity under mountains, 330; on 
terrestrial rigidity, 341, 342; 
on central density, 345. 

Precession, effects of, 285, 290. 

Precipitation, of planets, 478, 
621; on temporary star, 516, 
518 ; Kant's doctrine of, 586. 



Prel, du, on habitability, 497. 

Prenebular stage, 539. 

Pressure causing central solidifi- 
cation, 220. 

Pressure, lateral, in orogeny. 
See "Wrinkling," ''Plica- 
tions," etc. 

Preston, S. T.,on Lodge's views, 49. 

Prevost, C , on a wrinkling crust, 
296. 

Primitive earth, 558-63. 

Primitive wrinkles meridional, 
254; tidal phenomena, 264. 

Proctor, R. A., on zodiacal light, 
24; on nebular theory, 194; on 
lunar changes, 394 ; on Jupiter, 
431; on ultra-Jovian planets, 
443; on habitability, 497. 

Projectile force on moon, 400. 

Prolateness, tidal, 130, 226; of 
moon, 407. 

Protogffia of Leibnitz, 558. 

Purgatory action of tide, 400. 

Purpose not excluded, 197. 

Pyrolithic crust, 365, 366. 

Q 

Quantitative relations of tides, 

228. 
Quaternary period, cold of, 289. 
Queengouck. meteoric fall at, 11, 

12. 



Races, antiquity of, 379. 

Radial shrinkage, 303. 

Radial streaks on moon, 391 ; 
cause of, 403. 

Radius of gyration, 162-3, 437. 

Radius vector, 107, 124. 

Rafinesque cited, 572. 

Rains, first descent of, 273, 327; 
on moon, 401. 

Ramsay, And., on time ratios, 
364." 

Ranges of mountains, 305; im- 
possible on c n t r a c t i o n a 1 
theory, 308. 

Rankine on reconcentration of 
energy, 492. 



IITDEX. 



637 



Rate of downward increase of 
heat, 376. 

Rate of planetary cooling, 216. 

Rayet and Wolfe quoted, 514. 

Reade, T. M., on age of the earth, 
180; on continental erosion, 
373, 374. 

Recession of planets, 160; of tide- 
producer, 239; of moon traced 
backward, 259, 326; of Niagara 
falls, 369 seq, ; of St. Anthony 
falls, 372; of lake blutt's, 374, 
378. 

Reclus, E., cited, 373. 

Reconcentration of energy in our 
system, 207. 

Red spot on Jupiter, 429. 

Refrigeration, final, 484; deduc- 
tive views on, 487. 

Reichenbach on meteoric dust, 8, 
76; on meteors, 75-6. 

Relief of internal pressure, 345. 

Resisting medium in space, in- 
fluence of on nebulcie, 104; on 
satellites, 169 ; on planets, 477. 
See "'Matter in space." 

Respighi on zodiacal light, 24. 

Retardation of orbital motion, 
281. 

Retardation, of rotary motion 
from lagging tide, 232-9, 404; 
on the moon, 248, 396 seq., 404; 
from surface fluids, 250; of 
earth's rotation traced back- 
ward, 250 ; effects of, 278, 473-5 ; 
how produced, 405; on Jupiter, 
435-7; on ultra- Jovian planets, 
447 ; amount of, 474. 

Retral movement of tide, 234; 
causes meridional structure, 
253, 254. 

Retrograde rotation, how result- 
ing, 123 seg., 135, 157; alleged 
necessary in primitive stage, 
127; tendency from centrifugal 
force, 133 ; case of in Uranian 
system, 153-8 ; may result from 
collisions, 120, lo7; or from 
formative conditions (Fave), 
158. 

Reversal of spectroscopic lines,40. 



Revivification of a cosmos, 491, 
621; Spencer on, 492; Rankine 
on, 492; Kant on, 492, 586; 
Clausius on, 493. 

Riccioli on crater Jjinnc, 392. 

Richthofen cited, 354. 

Ricketts, C, on subsidence of 
crust, 316. 

Rigidity of earth maintained, 340, 
342 ; tested by tides, 342-3. 

Ring, abandonment of, 110, 613; 
width of. 111; discoid form of, 
alleged, 111-2; involving entire 
nebula, 117; stratification of, 
119, 176, 582; rupture and 
spheration of, 119-42, 614; in- 
stability of, 121; alleged im- 
probable, 186; conception of, 
in cosmogony, 620. 

Rivers, trends of, 353. 

Roche, on zodiacal light, 25; on 
Saturnian rings, 168; on the 
origin of the solar system, 214. 

Rocks, thickness of, 359 seq. ; ab- 
sorption by, 461 seq. 

Roots of mountains, 321. 

Roscoe on spectral analysis, 40. 

Rosmini cited, 553. 

Rosse, Lord, telescope of, 36; on 
lunar temperatures, 381, 414. 

Rotation of nebulse, 94-106; with- 
out impact, 98, 118; of mass 
resulting from spheralion, 121 ; 
influonced by cosmic tides, 129; 
influenced by external attrac- 
tions, 131; summary of princi- 
ples on, 134; alleged without 
adequate cause, 170. 

Rotation of planets, effect of 
changes in, 278 ; tidally retard- 
ed, 232-9. 

Rotation of earth in primitive 
times, 259. 

Rutherford on composition of 
stars, 191. 



Saemann, L., cited, 621; on ab- 
sorption of fluids, 382, 465, 468; 
on depth of ocean, 466 ; error 
of, 466. 468. 



638 



II^DEX. 



Saigev on the constitution of 
matter, 66. 

Satellites, tides on, 248, 438: con- 
ditions of detachment of, 262; 
Jovian tides caused by, 435; 
tides on, 438, 458 ; varying light 
of, 440; Jovian, water-covered, 
441: 'synchronous motions of. 
477, 616. 

Saturn, why ha^^ng several satel- 
lites, 262 ; physical condition of. 
442, 443-8; an ice-covered 
planet. 446; in Kant's theory, 
576, 579. 

Saturnian rings, 35, 482 ; rotation 
of, 168; not continuous, 185; 
disintegration of, 483 ; Kant on, 
581. 

Schellen on spectral analysis, 39; 
on nebulae, 44, 88, 117.* 

Schiaparelli on meteoric orbits, 
17; on comet of 1882 h, 31; on 
cometary origin of meteors, 33. 

Schmeizer cited, 330. 

Schmidt, J, F. J., on meteoroids, 
21 ; on comet of 1882 h, 31 ; on 
map of moon, 385: on crater 
Linne, 392. 

Schroter on Venus, 423 ; on Mer- 
cury, 425. 

Schuster on meteoric dust, 11 ; on 
Locky^r's views concerning 
matter, 49. 

Scintillations of stars, 69. 

Scrope, Poulett, on volcanic moun- 
tains, 330. 

Secchi on zodiacal light, 24; on 
nebulae, 45; on crater Linue, 
392; on Martial atmosphere, 
417; on Jovian satellites, 440; 
on double stars, 513; on solar 
spots. 520; on tvpes of stars, 
522, 529. 

Secondaries, rotations of, 125. 

Sedgwick on a wrinkling crust, 
295. 

Sedimentation along geosvncli- 
nals, 314-9, 324, 327; insuffi- 
ciency of theory of, 317. 

Sediments, a measure of time, 
356, 451; from rivers, 453. 



Seismism from tidal action, 325, 
348. 

Selenography, 385 seq. 

Seleucus cited, 551. 

Shrinkage, from cooling, 302; ra- 
dial, 303 ; as cause of accelera- 
tions, 359. See '"Wrinkling." 

Sickle-shaped nebula?, 43, causes 
of, 102. 

Siemens, W., on matter in space, 
57; on perpetuation of sun's 
heat, 57; criticisms on, 61; in 
reply to criticisms, 62, 63 ; fur- 
ther references on, 65. 

Silicates floating, 219. 

Simmons. G. W., on comet of 
1881, 29. 

Sirian phase, 541. 

Sirius the centre of Milky Way, 
589. 

Skinner, A. X., on comets, 29. 

Slaughter, W. B., on nebular ro- 
tation, 94; on angular velocity.. 
109; against nebular theory, 
153; basing objection on peri- 
odic times, 158; on angular 
velocities, 159; on rotary 
motion, 170; on inclinations 
of orbits, 171; on densities 
of outer planets, 177. 

Slipping of crust, 308-10. 

Snow on Mars, 416. 

Solar phase, 542. 

Solar System, origin of, 145. 

Solar tides contributing to separa- 
tion of moon, 260. See "Sun." 

Solidification, at surface, 218; at 
centre, 220; at centre, not a 
normal freezing, 271, 346; un- 
der pressure, 270 ; rationale of, 
271. 

Solidity, a relative j)roperty, 223 ; 
of a planet supposed necessarv, 
220. 

Soret's formula, 412. 

Spectra, classes of, 38 : of comets, 
27; of nebulae, 42-8, 192, 531; 
of fixed stars, 191, 522 seq., 
532; significance of nebular. 
192, 532. 

Spectroscope explained, 37. 



II^DEX. 



639 



Spencer, H., on spiral nebulas, 
102; dn origin of asteroids, 177; 
on comets, 181 ; on implications 
of nebular cosmogony, 197 ; on 
equilibration, 488; on restora- 
tion of cosmos, 492, 494. 

Spheration of nebular rings, 119- 
42, 614, 620. 

Spiller on nebular theory, 212-4. 

Spiral nebula?, 42, 44; causes of, 
99-102, 104. 

Spiro-annular nebulae, 44. 

Spots on sun, 520, 556. 

Sprengel air pump, 201. 

Stage of development, of planet, 
216; of Jupiter, 429, 430, 431; 
on ultra-Jovian planets, 446. 

Stages of world life, 438-44. 

St. Anthony gorge, 372, 378. 

Stars, multiple, 511; temporary, 
513-18; variable, 518; grada- 
tions of, 522; distribution of 
substances among, 525; heat 
of, 526; two stages in life of, 
526; darkened 560. 

Steam, in mountain making, 292, 
325 ; limit to elasticity of, 293-4. 

Steel, specific gravity of, 218; 
flotation of, 218. 

Stellar nebulae, 47. 

Stellar stage, 541. 

Stellation, incipient, 53. 

Steno cited, 563. 

Stevenson, J. J., on desiccation, 
471. 

Stockwell, J. N., on orbital incli- 
nations. 173; on eccentricitv, 
368. 

Stone, E. J., on tidal retardation, 
474. 

Storm secular, on eai-th, 272, 327; 
on moon, 401 ; on Jupiter, 433 ; 
on sun, 490. 

Strabo on upheavals, 292. 

Strata, thicknesses of, 350 seq. ; 
table of, 363. 

Stratification of a ring, 119, 176, 
582. 

Struve, Otto, on nebulas, 42, 88; 
on Saturn's rings, 483; on 
double stars, 512. 



Struve, W., on double stars, 512. 

Studer cited, 339. 

Submeridional trends. See " Me- 
ridional." 

Subsidence of ocean's bottom, 277, 
314-9; under load of sediments, 
314-9; on removal of load, 
317. 

Suess on mountain making, 294. 

Sulphur showers, 7. 

Sun, central density of,' 162; ro- 
tary velocity of, 166; density 
of, less than formerly, 190; 
tides caused by, 247, 250, 475; 
refrigeration of, 484r-7, 489; as 
a variable star, 519; Kant's 
doctrine of, 587. 

Superficial solidification, 218. 

Swarms of meteoroids, 17 seq. ; 
gathering of, 72. 

Swedenborg, E., on cosmology, 
566. 

Swift, L., on intra-Mercurial 
planets, 216. 

Sylvestri on a dust fall, 11. 

Synchronistic motions, 130-4; ul- 
timate, 134, 248, 473-7; on 
Mercury, 250; on the earth, 
251; primitive, of earth and 
moon, 259; of moon, 396 seq., 
404, 557, 580, 615; of Jovian 
satellites, 439. 

Synchronistic phase, 544. 

Svnclinal structure in mountains, 
"314-9. 

Synclinorium, defined, 322: com- 
pleted, 328. 



Tacchini on atmospheric dust, 11. 

Tails of comets, 77, 78. 

Tangential pressure in orogeny. 
See "Wrinkling," "Plica- 
tions," etc. 

Tebbutt on comet of 1881, 29. 

Temperature, lowering of, 485; 
of earth's interior, 307. 

Temporary stars, 513-8, 543, 609. 

Tenuity of primitive nebula, 
alleged too great, 184; calcu- 
lations on, 200. 



640 



li^DEX. 



Terrace formation, rate of, 374. 

Terrestrial phase, 548. 

Theophilus crater, 338. 

Thickness of mountain strata. 
317. 

Thicknesses of formations, 363. 

Thomson, J., on freezing point. 
270. 

Thomson, Sir William, on heat 
of meteors, 16; on meteoric 
orbits, 17; on the ether, 52, 54, 
55 ; on solar heat, 81 ; on age 
of the world, 179, 356, 364; on 
solidifying minerals, 218; on 
increase of temperature down- 
ward, 221; on terrestrial ob- 
lateness, 267 ; on freezing point 
under pressure, 270, 272; on 
unequal rate of rotation, 279; 
on geological climates, 290 : on 
a problem in thermics, 305; on 
change of axis, 334; on inter- 
nal liquidity, 340, 342; on 
liquidity from crushing, 347; 
on measurement of tides, 350; 
on effect of ice covering, 376; 
on tidal retardation, 473; on 
constitution of comets, 482; on 
colder climates, 486, 487; on 
dissipation of energy, 489 ; on 
A'ortex atoms, 569. 

Thomson, Sir Wyville, on ocean 
bottom. 302 ; on depth of ocean. 
466. 

Thought in the cosmos, 197; 
unity of, 508. 

Tidal action in planetary history, 
222-69 ; three general cases of, 
225; general effects of, 230; re- 
ciprocity of, 245-6; detaching- 
moon, 260; erosion by, 268; in 
mountain making, 325. 

Tidal evolution of moon, 395 seq. 

Tides, cosmic in a nebular sphe- 
roid, 129; crushing influence 
of, 131 ; synchronistic tendency 
of, 134, 248; action of, accord- 
ing to Spiller, 213; action of, 
in planetary history, 222-69; 
some elementary principles of, 
222; theories of, 225: oceanic 



conditions of, 225; deforraa- 
tive, 226; compound, 226; film. 
227; quantitative relations of, 
228; resulting from centrifu- 
gal action, 229 ; lagging of, 
231; sliding retrally, 233, 253; 
translatory motion of, 234, 351 ; 
anticipation of, 234; this great- 
est along equator, 235 ; discord- 
ant, 239; causing recession of 
tide producer, 239 ; on tide pro- 
ducer, 246; caused by sun, 247; 
causing synchronous motions, 
248; geal, on the moon, 248, 
249 ; on satellites, 248 ; meridi- 
onal structure caused by, 252- 
4; producing outflows of mol- 
ten matter, 255; crushing in- 
fluence of, 255; marine, in 
early history, 256: erosion by, 
268 ; influence of, in mountain 
making, 320; beneath the 
crust, 336 ; used to test earth's 
rigidity, 342, 343; connected 
with earthquakes, 348; action 
of. on moon, 383 seq.; geal. 
height of, on moon, 384; action 
of, after incrustation, 398, 404; 
amount of, on Mars, 417 ; gen- 
eral formula for, 418; influ- 
ence of, on Venus, 420; influ- 
ence of on Mercury, 424; on 
Jupiter, 433. 434-6; on Jovian 
satellites, 438; on ultra-Jovian 
planets, 447; retardation by, 
on earth. 474; solar, on earth, 
475. 

Time, geological, 355 seq. ; diffi- 
culties of numerical calcula- 
tions of, 377 : summary of re- 
sults on, 377-8. 

Time ratios, 356; table of, 365. 

Tissandier. G., oil atmospheric 
dust, 6, 9, 11. 

Todd. J. E., on changes in rota- 
tion, 279. 

Trades and anti-trades, 260. 

Trade winds on Jupiter. 428. 

Trends, meridional, 252, 253; in 
the earth's structure, 350. 

Trifid nebula, 91. 



IN^DEX. 



641 



Trouvelot, L., drawings bv, 42, 
90, 91. 

Trowbridge, D., on nebular an- 
nulation, 113; on periodic 
times, 158; on density of solar 
nebula, 161-8; on rotary velo- 
city, 165; on the asteroidal 
ring, 177. 

Twisden, I. F., on change of 
axis, 334. 

Tvcho crater, 389; radial streaks 
^of, 390, 404. 

Types of stars, 522. 

u 

Ueberweg cited, 553. 

Ultra-Jovian planets, 442; ad- 
vanced stage of, 444-8 ; cosmic 
periods on, 445; ice-covered, 
446. 

Ultramundane corpuscles, 620. 

Unity of the world, 592. 

Universe, evolution of, not im- 
plied, 196. 

Upheaved by aeriform agents, 
292. 

Upheaval of synclinoiium, 818. 

Uranian system, 158 seq., 157. 



V 



Vapor, first condensation of, 272. 

Vapors beneath crust, 292, 323. 
325. 

Variable phase, 542. 

Variable stars, 518. 

Velocities of zones of a nebular 
ring, 123. 

Velocity, angular, 109; increases 
with contraction, 159 ; changes 
in, affecting planetary condi- 
tions, 278. 

Velocity, linear, 109; in parts of 
ring, 123; increases with con- 
traction, 159 ; passage of, from 
developmental to Keplerian, 
160, 166 ; of hvdrogen molecules, 
184. 

Vents, volcanic. See ''Craters." 

Venus, inclination of axis of, 129 ; 
tides on, 250; why having no 



satellite, 262; apsides . of , 422 ; 

erosion on, 457; habitabilitv 

of, 500. 
Verifications of nebular theory, 

147. 
Viscosity affecting tides, 225, 231, 

241, 244, 246. 
Vogel on Lockyer's views, 49. 
Volcanic ranges, 831. 
Volcanic vents along njountain 

axes, 335. 
Vortical conception in cosmog- 
ony, 619. 
Vortices of Descartes, 555-6; of 

Leibnitz, 564; of Swedenborg, 

566. 
Vulcan (planet), 215. 
Vulcanism from tidal action, 325. 

w 

Wabble in earth's axis, 866-7. 
Wallace, A. R., on geological 

climates, 290. 
Waltershausen on law of density, 

345. 
Warring, C. E., on forces of 

nature, 223. 
Water, first condensation of, 272, 

327; on moon, 401. 
Watson, J. C, on intra-Mercurial 

planets. 215. 
Wave lengths of light, 37. 
Wave theory of tides, 225. 
Weakness, lines of, in wrinkling. 

299. 
Whewell, W., cited, 551, 566; on 

plurality of worlds, 497. 
Whirlpool motion in a nebula, 

209. 
Whiston, W., on the flood, 583. 
White, C. A., on Laramie, 364. 
White, L C, cited, 361. 
White stars, 522. 
Whitnev, J. D., on mountain 

making, 294, 817, 832; on 

thickening of formations, 317; 

on desiccation of continents, 

471 ; on changed climates, 485 ; 

on lava floods, 517. 
Width of nebular ring, 111-7. 
Wilkes on zodiacal light, 26. 



41 



642 



IKDEX. 



Williams, A, S., on lunar changes, 
394. 

Williams, H. S., on distribution 
of faunas, 281. 

Williams, W. M., on the matter 
of space, 55; on solar heat, 55; 
on floating iron, 219 ; on cool- 
ing cinder, 409; on Mercurv, 
423. 

Wilson on comet of 1882 b, 30. 

Winchell, A., cited, 609; on dis- 
sociation, 471 ; on final refriger- 
ation, 488; on cosmical even- 
tualities, 490; on stages of 
world life, 538. 

Winchell, N. H., on St. Anthony's 
Falls, 372. 

Winlock on comet of 1882 b, 31 

Winnecke's comet resisted, 429. 

World stuff, 48-65. 

Worthen, A, H., on distrbution 
of faunas, 281. 

Wright, A. W,. on zodiacal light, 
24. 

Wright, Gr. F., on geological 
time, 378. 

Wright Thomas, on cosmogony, 
572, 589. 



Wright, T. F., on Swedenborg, 

566, 571. 
Wrinkles, priinitive, meridional, 

254; in bottom of ocean, 301; 

later sometimes transmeridion- 

al, 326. 
Wrinkling crust, theory of, 294- 

314, 324; illustration' of, 297-8, 

299, 300; difficulties of theory 

of, 298-9. 
Wurtz on mashing of rocks, 320. 



Young, C. A., on heat of nebulae, 
81 ; on periodic time of Phobos, 
168 ; on solar spots, 520. 
! Young, Dr. T., on the ether, 58- 
66. 

! z 

: Zodiacal light, 23, 482, 484; polar, 
iscopic indications of, 23 ; Kant 
on, 583 ; Laplace on, 615. 

i Zollner on luminosities, 432; on 

i variable stars, 519. 521. 

I Zone of molten matter, 220, 344. 
Zones of climate affected by obli- 

i quity of axis, 283. 




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